BU-409: Charging Lithium-ion

Find out how to prolong battery life by using correct charge methods.

Charging and discharging batteries is a chemical reaction, but Li-ion is claimed to be the exception. Battery scientists talk about energies flowing in and out of the battery as part of ion movement between anode and cathode. This claim carries merits but if the scientists were totally right, then the battery would live forever. They blame capacity fade on ions getting trapped, but as with all battery systems, internal corrosion and other degenerative effects also known as parasitic reactions on the electrolyte and electrodes till play a role. (See BU-808b: What causes Li-ion to die?.)

The Li ion charger is a voltage-limiting device that has similarities to the lead acid system. The differences with Li-ion lie in a higher voltage per cell, tighter voltage tolerances and the absence of trickle or float charge at full charge. While lead acid offers some flexibility in terms of voltage cut off, manufacturers of Li-ion cells are very strict on the correct setting because Li-ion cannot accept overcharge. The so-called miracle charger that promises to prolong battery life and gain extra capacity with pulses and other gimmicks does not exist. Li-ion is a “clean” system and only takes what it can absorb.

Charging Cobalt-blended Li-ion

Li-ion with the traditional cathode materials of cobalt, nickel, manganese and aluminum typically charge to 4.20V/cell. The tolerance is +/–50mV/cell. Some nickel-based varieties charge to 4.10V/cell; high capacity Li-ion may go to 4.30V/cell and higher. Boosting the voltage increases capacity, but going beyond specification stresses the battery and compromises safety. Protection circuits built into the pack do not allow exceeding the set voltage.

Figure 1 shows the voltage and current signature as lithium-ion passes through the stages for constant current and topping charge. Full charge is reached when the current decreases to between 3 and 5 percent of the Ah rating.

Charge stages of lithium-ion

Figure 1: Charge stages of lithium-ionLi-ion is fully charged when the current drops to a set level. In lieu of trickle charge, some chargers apply a topping charge when the voltage drops.

Courtesy of Cadex

The advised charge rate of an Energy Cell is between 0.5C and 1C; the complete charge time is about 2–3 hours. Manufacturers of these cells recommend charging at 0.8C or less to prolong battery life; however, most Power Cells can take a higher charge C-rate with little stress. Charge efficiency is about 99 percent and the cell remains cool during charge.

Some Li-ion packs may experience a temperature rise of about 5ºC (9ºF) when reaching full charge. This could be due to the protection circuit and/or elevated internal resistance. Discontinue using the battery or charger if the temperature rises more than 10ºC (18ºF) under moderate charging speeds.

Full charge occurs when the battery reaches the voltage threshold and the current drops to 3 percent of the rated current. A battery is also considered fully charged if the current levels off and cannot go down further. Elevated self-discharge might be the cause of this condition.

Increasing the charge current does not hasten the full-charge state by much. Although the battery reaches the voltage peak quicker, the saturation charge will take longer accordingly. With higher current, Stage 1 is shorter but the saturation during Stage 2 will take longer. A high current charge will, however, quickly fill the battery to about 70 percent.

Li-ion does not need to be fully charged as is the case with lead acid, nor is it desirable to do so. In fact, it is better not to fully charge because a high voltage stresses the battery. Choosing a lower voltage threshold or eliminating the saturation charge altogether, prolongs battery life but this reduces the runtime. Chargers for consumer products go for maximum capacity and cannot be adjusted; extended service life is perceived less important.

Some lower-cost consumer chargers may use the simplified “charge-and-run” method that charges a lithium-ion battery in one hour or less without going to the Stage 2 saturation charge. “Ready” appears when the battery reaches the voltage threshold at Stage 1. State-of-charge (SoC) at this point is about 85 percent, a level that may be sufficient for many users.

Certain industrial chargers set the charge voltage threshold lower on purpose to prolong battery life. Table 2 illustrates the estimated capacities when charged to different voltage thresholds with and without saturation charge. (See also BU-808: How to Prolong Lithium-based Batteries.)

Charge V/cell

Capacity at
cut-off voltage*

Charge time

Capacity with full saturation











120 min

135 min

150 min

165 min

180 min






Table 2: Typical charge characteristics of lithium-ion. Adding full saturation at the set voltage boosts the capacity by about 10 percent but adds stress due to high voltage.

* Readings may vary

When the battery is first put on charge, the voltage shoots up quickly. This behavior can be compared to lifting a weight with a rubber band, causing a lag. The capacity will eventually catch up when the battery is almost fully charged (Figure 3). This charge characteristic is typical of all batteries. The higher the charge current is, the larger the rubber-band effect will be. Cold temperatures or charging a cell with high internal resistance amplifies the effect.

Figure 3: Volts/capacity vs. time when charging lithium-ion.
The capacity trails the charge voltage like lifting a heavy weight with a rubber band.

Courtesy of Cadex

Estimating SoC by reading the voltage of a charging battery is impractical; measuring the open circuit voltage (OCV) after the battery has rested for a few hours is a better indicator. As with all batteries, temperature affects the OCV, so does the active material of Li-ion. SoC of smartphones, laptops and other devices is estimated by coulomb counting. (See BU-903: How to Measure State-of-charge.)

Li-ion cannot absorb overcharge. When fully charged, the charge current must be cut off. A continuous trickle charge would cause plating of metallic lithium and compromise safety. To minimize stress, keep the lithium-ion battery at the peak cut-off as short as possible.

Once the charge is terminated, the battery voltage begins to drop. This eases the voltage stress. Over time, the open circuit voltage will settle to between 3.70V and 3.90V/cell. Note that a Li-ion battery that has received a fully saturated charge will keep the voltage elevated for a longer than one that has not received a saturation charge.

When lithium-ion batteries must be left in the charger for operational readiness, some chargers apply a brief topping charge to compensate for the small self-discharge the battery and its protective circuit consume. The charger may kick in when the open circuit voltage drops to 4.05V/cell and turn off again at 4.20V/cell. Chargers made for operational readiness, or standby mode, often let the battery voltage drop to 4.00V/cell and recharge to only 4.05V/cell instead of the full 4.20V/cell. This reduces voltage-related stress and prolongs battery life.

Some portable devices sit in a charge cradle in the ON position. The current drawn through the device is called the parasitic load and can distort the charge cycle. Battery manufacturers advise against parasitic loads while charging because they induce mini-cycles. This cannot always be avoided and a laptop connected to the AC main is such a case. The battery might be charged to 4.20V/cell and then discharged by the device. The stress level on the battery is high because the cycles occur at the high-voltage threshold, often also at elevated temperature.

A portable device should be turned off during charge. This allows the battery to reach the set voltage threshold and current saturation point unhindered. A parasitic load confuses the charger by depressing the battery voltage and preventing the current in the saturation stage to drop low enough by drawing a leakage current. A battery may be fully charged, but the prevailing conditions will prompt a continued charge, causing stress.

Charging Non-cobalt-blended Li-ion

While the traditional lithium-ion has a nominal cell voltage of 3.60V, Li-phosphate (LiFePO) makes an exception with a nominal cell voltage of 3.20V and charging to 3.65V. Relatively new is the Li-titanate (LTO) with a nominal cell voltage of 2.40V and charging to 2.85V. (See BU-205: Types of Lithium-ion.)

Chargers for these non cobalt-blended Li-ions are not compatible with regular 3.60-volt Li-ion. Provision must be made to identify the systems and provide the correct voltage charging. A 3.60-volt lithium battery in a charger designed for Li-phosphate would not receive sufficient charge; a Li-phosphate in a regular charger would cause overcharge.

Overcharging Lithium-ion

Lithium-ion operates safely within the designated operating voltages; however, the battery becomes unstable if inadvertently charged to a higher than specified voltage. Prolonged charging above 4.30V on a Li-ion designed for 4.20V/cell will plate metallic lithium on the anode. The cathode material becomes an oxidizing agent, loses stability and produces carbon dioxide (CO2). The cell pressure rises and if the charge is allowed to continue, the current interrupt device (CID) responsible for cell safety disconnects at 1,000–1,380kPa (145–200psi). Should the pressure rise further, the safety membrane on some Li-ion bursts open at about 3,450kPa (500psi) and the cell might eventually vent with flame. (See BU-304b: Making Lithium-ion Safe.)

Venting with flame is connected with elevated temperature. A fully charged battery has a lower thermal runaway temperature and will vent sooner than one that is partially charged. All lithium-based batteries are safer at a lower charge, and this is why authorities will mandate air shipment of Li-ion at 30 percent state-of-charge rather than at full charge. (See BU-704a: Shipping Lithium-based Batteries by Air.).

The threshold for Li-cobalt at full charge is 130–150ºC (266–302ºF); nickel-manganese-cobalt (NMC) is 170–180ºC (338–356ºF) and Li-manganese is about 250ºC (482ºF). Li-phosphate enjoys similar and better temperature stabilities than manganese. (See also BU-304a: Safety Concerns with Li-ion and BU-304b: Making Lithium-ion Safe.)

Lithium-ion is not the only battery that poses a safety hazard if overcharged. Lead- and nickel-based batteries are also known to melt down and cause fire if improperly handled. Properly designed charging equipment is paramount for all battery systems and temperature sensing is a reliable watchman.


Charging lithium-ion batteries is simpler than nickel-based systems. The charge circuit is straight forward; voltage and current limitations are easier to accommodate than analyzing complex voltage signatures, which change as the battery ages. The charge process can be intermittent, and Li-ion does not need saturation as is the case with lead acid. This offers a major advantage for renewable energy storage such as a solar panel and wind turbine, which cannot always fully charge the battery. The absence of trickle charge further simplifies the charger. Equalizing charger, as is required with lead acid, is not necessary with Li-ion.

Consumer and most industrial Li-ion chargers charge the battery fully. They do not offer adjustable end-of-charge voltages that would prolong the service life of Li-ion by lowering the end charge voltage and accepting a shorter runtime. Device manufacturers fear that such an option would complicate the charger. Exceptions are electric vehicles and satellites that avoid full charge to achieve long service life.

Simple Guidelines for Charging Lithium-based Batteries


Last updated 2018-04-24


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Comments (563)

On November 10, 2010 at 3:39am
Adley wrote:

Super post there! Comprehensive and well collated material. Thanks for sharing.

On November 11, 2010 at 7:41am
Grosser wrote:

Very usefull information here, good thing I fond this page first before designing a charger for my custom-made battery pack.

P.S. You’re alwais talking about a 4,2V like they are the the standardwhat about 3,6V cells?

On November 12, 2010 at 3:52pm
Jason wrote:

Facinating stuff, although I doubt I will ever have the ambition to put it use.

On November 21, 2010 at 6:45am
Mike wrote:


3.6 is the nominal delivery voltage of a Li-ion cell, while 4.2 is the max charging voltage. They are the same battery. It’s the same situation with other battery chemistries, e.g. for a 12V lead-acid battery, you’d be charging to ~14V

On November 21, 2010 at 7:22pm
Paul Smith wrote:

My Li-ion battery is used in a Canon 50D DSLR camera;  The charger blinks to indicate the level of charge.  The indications are 1-blink series, 2-blink series, 3-blink series, and steady-on to indicate full charge.  Often I leave the battery in the charger and go to bed if the LED is at the 2-blink state.  When I wake up 4 to 5 hours later, the LED may have been steady-on for 4 hours.  I have two questions.  (1)What harm am I doing to my battery by following this practice and (2)Is the battery fully-charged if I remove it from the charger as soon as the steady-on state is reached?

On November 22, 2010 at 8:15am
Eduardo wrote:

I need to do the following test:

1 Question;
Have my charge Battery is Full. How time (day) can battery disconnect?


2 Questions
What time need battery recharge for has charge Full ?.

PD: My power Supply is 3,7 volt

On November 23, 2010 at 6:26pm

what is the work of that circuit inside a lithium ion battery?

On November 24, 2010 at 7:29am
Eduardo wrote:

Thak You, unanswer.

The Batery is connected circuit 3,6 volt constant (regulable according to load) and this support a circuit for memory and a processor primary.

Thanks again.


On December 2, 2010 at 1:12am
Steve Webert wrote:

Does it benefit a lithium-ion or lithium-ion-polymer battery to periodically discharge it “fully” (ie, down to the above mentioned 2.7V-3.0V range)?

I have read several OEM’s offering differing strategies for optimizing battery life.

Thank you for your time and efforts—I very much appreciate the above instruction.

On December 9, 2010 at 2:02pm
Thomas Vargas wrote:

What about chargin vehicle batteries? This will be a big issue if they ever become popular.
How would the graph look if it were for vehicles?

On December 17, 2010 at 8:43pm
thomas micciantuono wrote:

Can lithium polymer cell phone batteries be over charged if left on charge to long and if left on to long will it diminish battery life.

On December 27, 2010 at 9:27pm
Andy wrote:

I’ve inherited an electric vehicle powered by two 38V/90Ah lithium-ion batteries.  The voltage of both packs read around 9V only!  The engine management system reports that a mere 21 hours of operation have been logged thus far.  Are these battery packs truly dead-DEAD or is it possible to resuscitate them again in one way or another?  Please advise.  Cheers.

On January 3, 2011 at 10:21pm
Flynn Siy wrote:

I am looking for alternative charges for my HTC Desire. The standard charger that came with it is 5V and 1000mah. Since the charger uses a standard micro USB tip, there are a lot of available chargers out there with different Amp rating. Is it advisable to get a low Amp rating such as 500mah, higher amp such as 1200mah or stick with the same 1000amp? Is slow charging better than fast charging?

On January 6, 2011 at 12:50am
Jerry Conrad wrote:

My HTC EVO cellphone shuts down when the discharge voltage reaches 3.6 volts. Isn’t this reducing the use-capacity of this battery quite a bit?

On January 6, 2011 at 9:59pm
Jovy Macaspac wrote:

I’ve read somewhere that a charger with a lower voltage rating (e.g., 3.2v) cannot recharge a lithium battery with a higher voltage rating (e.g., 3.7v). Is this true?  Something to do with electron transfer, I think… If this is true, I’m confused. How can a 3.7v charger charge a 3.2v battery to 4.2v if, when they reach the same voltage level (3.7v), it can no longer push said electrons around the battery?

Another question, if it’s alright:  USB chargers have a rating of 5v.  Would this cause problems with lithium batteries since as stated above, charging above 4.3v causes plating of the metallic lithium on the anode?

Thanks and more power!


On January 7, 2011 at 6:47pm
Mr. D wrote:

how can you trickle charge a 12v batt @ 2v trickle and get a full charge . the battery is like a tank, with a limitation of it"s rateing ie. 4.2v or 12v ,is the limit that the battery will hold, forceing anything over that will start to burn the core of the battery in one way or the other ... do i win a cuppie doll??

On January 9, 2011 at 1:44pm
Vass wrote:

@ Flynn Siy, the ratings of the charger mentioned misguiding me as the standard charger rating should be in terms of volts and Amps/milli amps(mA) but not in mAh. If your concern is about a charger(i’ll interpret it to 500mA/12mA ) then go for 1200mA. There’s no harm in it. If you go for 500mA, it’ll charge but it become hot due to it’s inability to supply the rating current(say 1000mA).This inturn drop the voltage. If your concern is about a battery(a standard battery rating will be in volts and mAh), go for either one but in reduction in back up, in case if you chose 500mAh.Hope it cleared your doubt.

On January 12, 2011 at 7:03am
Shiwakoti wrote:

How Li-ion battery gets recharged? Why at elevated temperature the battery life gets shortened? Does frequent charging pratice without being fully discharged affect bttery life span? Plz help..

On January 15, 2011 at 3:55am
Ike wrote:

“My HTC EVO cellphone shuts down when the discharge voltage reaches 3.6 volts. Isn’t this reducing the use-capacity of this battery quite a bit?”

—This is to protect the battery: further discharge could destabilize it and next charging could be risky (you may have heard of exploding LiIon batteries…).
Despite more strict cutoff liit, LiIons can store more energy than previous technologies iin same cell size, so you should not consider this a design fault/drawback, just a essential characteristic feature of this different chemistry.

Shiwakoti, you will find answers to your questions on the articles at this site: esp. in “Is lithium-ion the ideal battery?”. Shortly said, elevated temperature speeds up battery aging (it’s a chemical reaction a bit like how iron rusts faster in humid climate compared to dry circumstances) and it’s MUCH better to recharge often than let LiIons drain fully.

On January 15, 2011 at 5:43am
Shiwakoti wrote:

Thanks for the answer..

On January 23, 2011 at 1:08am


On January 23, 2011 at 1:31pm
Curt Eglin wrote:

Excellent material.  I now know how to properly charge a 3.7 volt Li-Ion pack I took out of a Blackberry phone that is since defunct.  Tnx.

On February 2, 2011 at 2:24pm
Mike wrote:

So in this article is states that Lithium Ion batterys are charged upto 4.2v, where each cell can handle 4.2v +/- .05v.  So the upperbound here is 4.25v to 4.15v.  So, if you have a charger that is push the cells to 4.21v or 4.22v, then it is theoretically fine.

“A continuous trickle charge above 4.05V/cell would causes plating of metallic lithium that could lead to instabilities and compromise safety. “

Here though you say that raising the cell above just over 4v may cause plating.  So by specification, charging lithium ion cells to 4.2v will cause plaiting?

On February 4, 2011 at 6:54am
captainirmak wrote:

i observe (via an application) that my smartphone is reaching till 4191 volts during re-charging the battery by usb cable.

can we say that battery is died a bit? cos it is not reaching 4.2 or above.

i know that it is very small numbers but curious about it.

and also what shold i do max charge the battery?

On February 4, 2011 at 2:21pm
Ken wrote:

The article mentions how dangerous it is to attempt charging cells that have been @<1.5v for just a few days. Well, that has not been in agreement with my experience. I occasionally salvage discarded Li-ion laptop battery packs…disassembling them to harvest the 18650’s for personal r/c and flashlight use. I commonly pull cells that are totally flat: 0v, sometimes even with polarity reversed by a few millivolts. In addition, some of the battery packs I ripped into were prehistoric by lithium chemistry standards (10 years+). More often than not all cells would recharge to their FULL original rated capacity and perform as new. I always test each cell individually with my iMAX B6 charger, manually putting them through at least a couple 500mA to 1Amp discharge/charge cycles. I have *never* experienced any safety nor reliability issues to date.

I would also like to brag of having had success restoring substantial capacity to the occasional cells that truly were worn. I will never share my method_IT’S MINE !_do not ask. ...Additionally, that procedure IS potentially dangerous and requires mandatory attentive supervision.

I suppose I’ve been laughing all the way to the battery bank. I know, horrible joke!

On February 11, 2011 at 1:30pm
TAS wrote:

What i have believed is keeping my laptop plugged in all the time at my desk and using the battery power in case of power failure or so. We have very frequent power cut-downs for brief spans. I also use BatteryCare to notify me of recalibration.
AFAIK Li-ion does not have memory effect and they have PMS circuit built-in so don’t overcharge. 
A vendor of notebooks recently opposed and recommended to cycle discharges and recharges regularly to keep the battery healthy and prolong its life.
What’s the bottom line?

On February 11, 2011 at 1:32pm
tas wrote:

What i have believed is keeping my laptop plugged in all the time at my desk and using the battery power in case of power failure or so does no harm to my battery pack. We have very frequent power cut-downs for brief spans. I also use BatteryCare to notify me of recalibration.
AFAIK Li-ion does not have memory effect and they have PMS circuit built-in so don’t overcharge. 
A vendor of notebooks recently opposed and recommended to cycle discharges and recharges regularly to keep the battery healthy and prolong its life.
What’s the bottom line?

On February 15, 2011 at 10:28am
Steven Hess wrote:

I just bought a Bushnell GPS and it has a Li-Ion battery pack. The instructions said to charge the li-Ion batteries for four hours. But upon plugging the charger to the batteries the green light immediatley came on, indicating a fully charged pack. But the pack is not charged at all. The unit will not turn on with these batteries. So my question is; Why is the charger displaying a Green LED when in fact the batteries need charged. And is there something I can do to make it start charging because the charger doesn’t charge when displaying a green light.

On February 15, 2011 at 1:06pm
Dan wrote:

Mike, I have been thinking of doing some EV experiments using some old laptop cells. They flat and packaged in plastic bags. What do you think about using this type of cell?

On February 16, 2011 at 12:24pm
Edward wrote:

i got a new phone. and it says b4 i do anything, i need to charge it for a total of 12 hours for it 2 run right, and battery life, blah blah…. but my question is, simple and plain… do i need to really charge it for the full 12 hours? can i just charge it until it says 100% charged, which would be in a hour or two…. i’ve google’d my question, and i’ve read mixed answers… “yes you should” “no, you don’t have to, because its a lithium-ion” whoop this, and whoop that…..

i would jus like a simpe answer.. yes or no… and why?

Thanx yous

On February 16, 2011 at 11:49pm
Samer wrote:

hi, i would like to know about the first charge lithium baattery ?
should i live chargim for 24h ?


On February 18, 2011 at 2:43am
Betty wrote:

Thanks so much.  All the new gadgets (laptops, cell phones, portable TV-DVD kits, etc) don’t specify anything about the Battery “rules’ like they used to in the day of NiCad and NiMH.  This article is very VERY informative and helpful.  NOW, i better start unplugging my laptop… thought i was ‘saving’ the battery by keeping it plugged in while using.  I guess i probably shouldn’t be charging my cell phone overnight for 8+hours either?

On February 19, 2011 at 2:33am
Ken wrote:

Great article, very informative. Can anyone help me with the following:
I have a Gibson Robot Guitar, the manufacturer states that it runs on:
(2 x 14500) 2.4v 2100mAh lithium rechargeable battery system.
These batteries have been run down for some time now and do charge, the manufacturer cannot replace them.
How can the voltage be 2.4v when the minimum cell voltage for lithium batteries is 3.6v What should I buy to replace these?

On February 25, 2011 at 9:12pm
marwan saade wrote:

dear sir
i have a vemar jiano helmet with integrated bluetooth. by mitake i’ve charged it with a nicd charger so the batterie was distroyed and does not work anynore.
when i opened the divice i found a li ion battery 3.7v 800ma reference stilo b001011.
please i would like to know if there is a way to fix it or recharge it again
if not can i use a a 1cell lypo battery to replace it

On February 28, 2011 at 11:14pm
to make money forex trading wrote:

You made some respectable points there. I looked on the internet for the issue and located most individuals will associate with together with your website.

On March 1, 2011 at 9:19am
BJ McGeever wrote:

So should I do my best to keep the battery at 40%? For instance I’ve been letting it hover around 40% by continually plugging and unplugging it. Is that a good idea?

On March 3, 2011 at 6:08pm




On March 10, 2011 at 2:31pm
Isidor wrote:

This article has been updated as of March 10, 2011 with all new information. Enjoy!

On March 10, 2011 at 8:07pm
Robert wrote:

Nice work Isidor.  Thank you.

On March 12, 2011 at 10:10am
Lee Kunkiw wrote:

Mar. 13, 2011
To : Robert

I am looking for a 24V bicycle dynamo.
Is it available ? Please help me if you possible.
Thank you.


On March 15, 2011 at 11:47am
TAS wrote:

What i have believed is keeping my laptop plugged in all the time at my desk and using the battery power in case of power failure or so does no harm to my battery pack. We have very frequent power cut-downs for brief spans. I also use BatteryCare to notify me of recalibration.
AFAIK Li-ion does not have memory effect and they have PMS circuit built-in so don’t overcharge.
A vendor of notebooks recently opposed and recommended to cycle discharges and recharges regularly to keep the battery healthy and prolong its life.
What’s the bottom line?

On March 17, 2011 at 8:22am
Subbu wrote:


I have a simple ARM7 gadget and I want to run it on the Li-ion batteries which are available cheap. Is there any singly IC chip solution which could
a. Charge the battery when connected to mains/ USB
b. Indicate the content of charge to ARM7 (ARM7 can query and stop working if there is no charge left to function properly)

With best regards,

On March 25, 2011 at 6:44pm
Francisco Bolivar wrote:

I have an elerctric bike with a 600w - 36v motor.
It uses a li-Ion battery.
Usually each time I use the bike its charge drops about 20% of the total battery charge.
1 - CHARGE THE BATTERY EACH TIME I USE THE BYKE (battery with 80% of charge)

On March 27, 2011 at 3:02pm
JimQ wrote:

I would like to make a battery pack charger for 4 Li ion cells.  Would it be detrimental to limiting the charger voltage to ..say..15 volts.  This would be within the voltage limit for each cell if the distribution is even.. However, if a cell is shorted there wpuld be excessove voltage on the other cells in the series string.  Would it be better to design the charger for 4.0 volt peak and charger the 4 cells in parallel?

On March 28, 2011 at 7:20am
Dominic Gill wrote:

Excellent article. Thanks.

On March 30, 2011 at 1:00pm

most dynamo give an AC ourput,
you could try to use a transformer to UP the voltaje

Michel Kun

On March 31, 2011 at 11:47am
Hemanth wrote:

How to remove the charging time li ion battery ? Is there any alternatives way ?

On April 10, 2011 at 12:22pm
Wayne Robey wrote:

Informative article but the voltage drop in stage 3 would indicate a cell in poor condition. A good cell will drop less.

My observation on using batteries after being badly discharged:
About 5 years ago I purchased 40 nearly unused 18X65 cells in 2 cell packs with protect circuit. They ware all discharged to cell voltages of .01 to 1.1 v. I charged them for 10 hrs at c/100 (Now I think c/10 would be OK) and 10% failed shorted. The remainder charged well at c/10 to 4.2 V. Letting them set 24 hrs, I looked at the voltage drop and classified the lowest 10% as weak. Then making a 12 V pack from the remainder I had 2 unused cells classified as good. I have had no failures though they have not been treated roughly. I checked the voltage on the unused cells today. Those marked weak are above 3.7V and those marked good are above 3.9V.

On April 11, 2011 at 4:33am
michael dalton wrote:

Hey guys,

Just want to get this clear in my head. When charging the battery up, I get a controller to put constant current into the battery, then when I sense 4.2v/cell, I get the controller to go into constant voltage (of 4.2) mode and the current will die away naturally till fully saturated?



On April 11, 2011 at 7:42pm
Wayne Robey wrote:

Michael, NO, the manufacturer recommends that when 4.2 v is reached, let the current fall to c/10 then turn it OFF. I think a constant voltage charge can be done but it takes a long time and must be done at a lower voltage. When the above charging is done and the battery sits 12 hours, measuring the voltage and setting the float voltage to that is safe and gives maximum capacity but that voltage goes down as the battery ages. A float voltage of 4.1 is reasonable to get best capacity but as the battery gets old, that MIGHT make it age faster. Using the 2 step process of charging at 4.2 v till the current reaches your chosen value (>= c/10) then dropping the voltage to a float value would be the way to quickly charge then float it.

On April 12, 2011 at 4:54am
michael dalton wrote:

Hey Wayne,

Thanks for the reply. So is the current we are measuring the battery current or the current from the charger.


On April 12, 2011 at 5:13am
michael dalton wrote:

Hey sorry Wayne I think I’m becoming confused. Do you apply a constant voltage in stage 2 until the current reaches c/10 OR manually bring the current down to c/10 with a controller?


On April 12, 2011 at 5:55pm
Erik wrote:

Why can the the battery pack in a Tesla automobile be charged considerably faster when the charging unit is 240v vs. 110-120v?

I iam a complete novice, and am wondering if higher voltage input decreases charging time.

Thanks for any insight you can offer.

On April 13, 2011 at 5:55pm
Wayne Robey wrote:

Not all Li cells are the same so the numbers I use below are for the most common ones, some can be charged much faster.
The algorithm is to check the voltage and if it is < ~3 charge at no more than c/10. If it is >3v charge with limits of c/2 and 4.2 volts until a current of c/10 is reached, then stop . As mentioned in the article a voltage < 4.2 increases battery cycle life, shelf life, and reduces discharge capacity for the current cycle. A charge rate < the maximum rated is easyer on the battery. I think charging with variable current is satisfactory if current is limited as specified on the data sheet and the voltage is limited to 4.1 volts. This is good for float charging and charging from a variable source.

There is no inherent reason. It was designed that way to account for commonly available power connections, commonly limited to 20A (use at < 80% of limit) at 120v but commonly available at 50 A or more at 240V.

On April 14, 2011 at 12:47am
Jayk wrote:

I am unable to decide which is better - to select a Li-ion battery pack with multiple cells or single cell. For example, how to choose between a 3.7V, 1500mAhr and a 7.4V, 1500mAhr ?

On April 18, 2011 at 9:41am

i am
got some PSP battery from HK
I measuered 4.8 volts on end of charge
4.5 volts after 3 days standing

THEN WHY IS 4.2VOLTS MAXIMUM in all litterature
is this value ABSOLETE???

the battery seem to work OK.

thanks in advance for any help or informations

On April 21, 2011 at 4:37am
Alex wrote:

Amazing website… well written .. very very useful
Great Job

On April 24, 2011 at 8:33pm
nash wrote:

Great article!!

On April 25, 2011 at 6:54am
zz wrote:

what happens if you let a li-ion battery connected indefinitely at 4.0V?

On May 3, 2011 at 2:36pm
Ryan wrote:

So I am building a solar powered usb charger for an android device. I know that my available curent and voltage at the time of charging will vary depending on the panel so in addition to overcharging I am wondering if capacitors to buffer power is necessary. I have also considered a 3000mAh battery with an integrated charging circuit would be better. That would offer me more consistent ouput to the device and be a contingency for a lack of or poor lighting. Any ideas would help. Kudos on the page, very informative.

On May 5, 2011 at 8:02am
Bilal nasir zargar wrote:

i brought a new battery sony lithium-ion NP-BG1, WHEN I BUY IT , IT WAS IN SLEEPING MOOD, i plugged the charger for charging, but it did not charge, so please suggest me what should i do…

On May 7, 2011 at 9:19pm
mike wrote:

Great article. Well written and very informative - just what i was looking for. Thanks and keep up the excellent work.

On May 8, 2011 at 8:35am
JimQ wrote:

Great informative article.  For a “12volt” pack, I would charge 3 or for Li Ion cells with a constant current source and limit the volts per cell by connecting a 4.0 volt zener diode across each cell.  This would allow parallel charging but also protect the cells from ‘over voltage’.  Does this make sense?  The total charging current would be limited by the charging source circuitry and shut off after all cells reached 4.0 volts.

On May 9, 2011 at 1:08pm
TONY wrote:

Li-Ion (Poli)bat
Min V=2.7V ? 3.0V
Midle=3.6-3.7 (Li-Ion Li-Pol)
end of Charging 4.2V Sel Kill 4.3V+
Kill it Fast 4.35 +

On May 9, 2011 at 1:41pm

what about voltajes for

On May 9, 2011 at 1:51pm
TONY wrote:

Higher charge voltages boost capacity but lower cycle life and compromise safety.
Li-ion battery to 4.20V/cell. This allows maximum runtime
We have limited information by how much lower charge voltages prolong battery life; this depends on many conditions, as we have learned. What we do know, however, is the capacities. At a charge to 4.10V/cell, the battery holds a capacity that is about 10 percent less than going all the way to 4.20V/cell. In terms of optimal longevity, a charge voltage limit of 3.92V/cell works best but the capacity would be low. Besides selecting the best-suited voltage thresholds, it is also important that the battery does not stay in the high-voltage stage for a long time and is allowed to drop after full charge has been reached.
V4.20 end of Charging 100 MA (Panasonic ?)

On May 9, 2011 at 2:04pm
TONY wrote:

4.20 400+ capacity 80%
4.25 400 bat capacity 25%
4.3v 250 Cycles 50%
4.35v 190 Cycles 25%

On May 12, 2011 at 4:07pm
Skip wrote:

My laptop has a battery rated at 10.8V, 85Wh, 8800mAh. The charger outputs 18.5V, 3.5A, and 65W. I have an old charger that is rated 19V, 3.4A and 65W. Would it be safe to use the old one?

On May 13, 2011 at 1:38am
Andrea wrote:


i want to charge a 7.5 v 400 mAh li-ion battery from a small solar panel (6V - 1W).
I would connect the solar panel and the battery with a voltage regulator or with a MPP circuit that fixed the output voltage adjusting the output current of the solar panel catching always the maximum power from it. In this way it’s difficult charge the battery using the constant current/constant voltage method because i can’t control the charge current and i haven’t enough power from the solar panel.
In conclusion the charging of the battery is done with a small and variable charge current. Is that a problem? Can i charge the battery always in slow charge fase and with a variable current? If yes, which are the drawbacks?
Thank you. regards!

On May 26, 2011 at 4:22am
Roy wrote:

Excellent!!! Love the detail…!

On May 26, 2011 at 6:54pm
edy wrote:

why lithium can perform fast charging between range 20% to 80% SOC only?
Why after 80% SOC charging became slow?

On June 12, 2011 at 4:27am
Joseph wrote:

My son and I have the same cell phone. His battery charge lasts 1 days and mine only one day. I came here to find out why. We thought it was because I was charging too frequently. I now believe its because I always left the phone on while charging whereas he turns his off. Thanks for the info!

On June 12, 2011 at 4:29am
Joseph wrote:

oops! 5 days vs 1 day…

On June 14, 2011 at 11:53pm
Nolan wrote:

Great article, thanks for the writeup.

One question: Would charging a Lithium battery with a higher amperage charger (but same voltage) cause any damage to the battery? I’m looking at +300mA to +500mA increase.

On June 15, 2011 at 9:53pm
Craig wrote:


I have a cell phone with a lithium battery.  Is it true that it is better to let the battery almost completely die before charging?  I was told the battery has a memory.  Someone also told me that was only true with NiCd.

On June 20, 2011 at 8:03am
Terry Bleasdale wrote:

nteresting article but it seems to be contradicted by information here:
which states that Lithium Polymer can be left on charge between bike rides without detriment.

Which is correct please?

On July 4, 2011 at 6:34am
determan wrote:

Hello, my protected 18650 cell faced a high current draw and the protection circuit went to sleep mode.. the cell now measures just 0V!.. Do anyone know how can I wake up such a cell?.. Your help will highly be appreciated.. thanks..

On July 26, 2011 at 4:31am
Javier wrote:

Hey, very good article.
1. Where it says “The battery is continuously being discharged to 4.20V/cell and then charged by the device” I think you mean “The battery is continuously being CHARGED to 4.20V/cell and then DISCHARGED by the device”
2.¿Its ok to charge to a safe level, say 80% (thus preventing minicycles and overcharging the battery) with the device on?
3.¿How can you tell if the charger and/or the device has taken measures to prevent minicycles,overcharges,etc..?

On July 26, 2011 at 2:30pm
Ümit wrote:

Very vey thaks. Usefull informations.

On July 28, 2011 at 3:38am
Amkul wrote:

Hi everyone

I just wanna ask some of the experts here, whether it’s is OK for me to charge a lithium-ion battery (let’s say a 2Ah), with a constant current of 50mA and a float voltage of 4.1V?

Despite the slow charging rate (longer time of course), would this work and would there be any other problems?

On August 10, 2011 at 6:50am
JC22 wrote:

So, let me just make sure i have this straight.

I am building a charger and here is my what i am doing:

1. When battery is first connected charge at c/5 (as recommended by battery manu)
2. While in this stage continually read the voltage i am charging at to produce this current.  (Question here: is this correct?  or do i need to shut off my charge voltage and wait about a second for voltage to settle to battery voltage then read?)
3. When the voltage i am CHARGING at hits 4.2 at this current i charge at a constant 4.2 volts from this point on until the current drops below c/100 (as recommended by battery manu), or the total charge time exceeds 10hrs (as recommended by manu).
4. When my current hits this low i simply cut out the charge.  Question - should i float the charge line at some value after charge?

So, basically i just want to make sure my method is basically correct.  Am i reading the correct voltage to determine when to stop fast charging and when i am fully charged should i just leave the charge line at high impedence or should i float it to some value?

On August 12, 2011 at 2:28pm
jin wrote:

again, huge amount of misleading info here doesn’t mean everything is wrong. The author actually read these comments, but doesn’t reply to them, as he has deleted my previous post regarding the reliability of the info presented in this page.

On August 12, 2011 at 2:36pm
jin wrote:

To JC22:

2, you don’t need to cut off your charging voltage to see the stage of your battery.
3, no true; you are risking over-charging the battery at c/100 and more than 10 hours.
4, you shouldn’t float charge a lithium battery
5, When you are fully charged which shouldn’t be, you are not a battery. you should just stop risking over-charging yourself.

On August 12, 2011 at 2:40pm
jin wrote:

To Amkul:
You can charge with low current, but you shouldn’t float charge it. float charge means keep charging without stop; you have cut the charging current when this current is lower than 50ma; or you risk over-charge your battery.

On August 12, 2011 at 2:44pm
jin wrote:

to Javier:

1, yes, you are right.
2, It is totally fine.
3, there is no way you can tell; other than taking apart the charger and reconstruct the circuitry yourself.

On August 12, 2011 at 2:46pm
jin wrote:

To determan:
If your battery doesn’t charge up in the charger, the circuit probably is damaged.

On August 12, 2011 at 2:49pm
jin wrote:

To Craig:
You can charge lithium any time; memory effect is for the very old nicd only.

On August 12, 2011 at 2:52pm
jin wrote:

To Nolan:
You can, but never charge with more than 1C; and that is if you have a 1800mah battery; you shouldn’t charge it with 1.8A (1800ma);

On August 12, 2011 at 2:53pm
jin wrote:

It is not true; If you use your cell more than your son; then obviously it will last shorter.

On August 12, 2011 at 2:58pm
jin wrote:

I am afraid that you can’t charge a 7.5V battery with only 6v solar panel. You need 8.35V, so you need a dc to dc booster with regulation,but charging the battery with variable current is fine.

On August 12, 2011 at 3:04pm
jin wrote:

To skip:
It depends on the charger; but if the output voltage of those 2 charges is more than 12.3 Volt, both are not safe to charge your 10.8v battery.


On August 12, 2011 at 3:07pm
jin wrote:

To Ryan:
Your battery is your buffer. no cap is needed.

On August 12, 2011 at 3:09pm
jin wrote:

To zz:
You will over-charge the battery. It will expose eventually.

zz wrote:
what happens if you let a li-ion battery connected indefinitely at 4.0V?

On August 12, 2011 at 3:18pm
jin wrote:

As I know, PSP uses 5 volts power source. This either means that there is an internal circuit in the battery that boost the voltage from 4.2 to 5+ volts; or the battery is not made out of lithium. Either case, your battery should be safe to use.

On August 12, 2011 at 3:21pm
jin wrote:

To Jayk:
Depends on your needed voltage and power; higher voltage means higher voltage and higher power stored.

Jayk wrote:
I am unable to decide which is better - to select a Li-ion battery pack with multiple cells or single cell. For example, how to choose between a 3.7V, 1500mAhr and a 7.4V, 1500mAhr ?

On August 26, 2011 at 4:19am
Garry D wrote:

An enterpreneor claiming, new technology can charge Lithium Ion Battery can charge eight times more life ????

Comments Please ???

On August 26, 2011 at 2:23pm
zz wrote:

you mean explode… interesting, I figured current must be 0 once voltages equalise, so no overcharge

On August 28, 2011 at 3:39am
jin wrote:

To zz:
we are not in a perfect world. The charging voltage maybe more than 4.20, which means there is current going into the battery, and explode it eventually. On the other hand, due to the age of the cell itself, it may not has its maximun capacity voltage of 4.2. Normally when you charge the cell to 4.2 volt, it will drop a little bit. If a 4.2 volt charging current is kept charging that battery, eventually heats and pressure will built up and explode the battery.

On August 28, 2011 at 3:42am
jin wrote:

To Garry D,
Yes. technically, it is possible.

On September 8, 2011 at 6:23pm
ray wrote:

if i have a 3.7volts li-ion battery what is the output specification of my battery charger?

On September 10, 2011 at 4:52am
Garry D wrote:

Which new company has come up with this 8 times more life For Lithium Ion Rechargable Battery.

On September 13, 2011 at 11:21am
zz wrote:

you misunderstood the question

On September 15, 2011 at 5:10pm
Sherri wrote:

I’m really not clear…..

I have a Dell laptop which I only use at home. Should I leave it plugged in? should I only plug it in when it needs to be charged? I have noticed that it has been getting very hot and at times the charger seems hot. We have been leaving it plugged in most days, then unplug it at night.

Thank you for clarifying for me!

On September 15, 2011 at 5:25pm
zz wrote:

Most likely 4.2V, but it is also limited in current.
jin, the charging voltage is 4V, no more

On September 16, 2011 at 9:45pm
jin wrote:

TO ray:

Output of your charger should be 4.2V at 200mA-1000mA

On September 16, 2011 at 9:47pm
jin wrote:

4.2V at 100ma-1000ma

On September 16, 2011 at 9:47pm
jin2 wrote:

4.2V at 100mA-1000mA

On September 16, 2011 at 9:50pm
jin2.0 wrote:

To ray :
4.2V at 100mA-1000mA

On September 17, 2011 at 7:05pm
zz wrote:

Most likely 4.2V, but it is also limited in current.
jin, you misunderstood my question

On September 20, 2011 at 6:48am
Itamir wrote:

Thank you very much. It helps me a lot. Very good material.

On September 21, 2011 at 11:59pm
zz wrote:

Most likely 4.2V, but it is also limited in current.
jin, you misunderstood my question

On September 24, 2011 at 11:23am
zz wrote:

Probably 4.2V, but it is also limited in current.
jin, you misunderstood my question

On September 25, 2011 at 11:36am
satyendra wrote:

hi evry1..
for my application of voltage(72V) , i connected 23 li-ion cells in series. each cell have 90 AH of capacity.now each and every cells have voltage have 3.3V.
so my question is that how would i know that what is the current SoC of the cells.
and second question is while charging it when current starts decreasing, at till what point of current i should wait for the complete charge.

please any1 help me in finding above.

On September 26, 2011 at 4:20pm
Mark Z. wrote:

Is slow charging (via USB-Port) better then fast charging (wall plug)?

On September 26, 2011 at 8:59pm
Garry D wrote:

I’ve not heard of any entrepreneur but there is a team of scientist at the DOE who are on the verge of expanding capacity 8x…


On September 30, 2011 at 4:04am
Peter wrote:

Great article, helped a lot. Do you have by chance a similar article about proper discharging a Li-ion cell? I’m especially interested in detecting the lower threshold where discharging should be stopped. A diagram similar to the one here would help a lot. Would you detect voltage? If yes, what is the low threshold? Would you detect internal resistance? (If the latter, how?)

On October 5, 2011 at 2:06pm
zz wrote:

Probably 4.2V, and also limited in current. Better measure.
jin, you’ve misunderstood

On October 19, 2011 at 10:22pm
tosvus wrote:

I bought a Li-ion battery/pack with charger (in the form of an adapter). Unfortunately, I mixed it up with another adapter, so I used a 12V-1.5a charger instead of the 12.6V-0.350A I should have used. I noticed that the battery only outputs 9V max now, with charge dropping rapidly. Did I permanently damage it?

On October 23, 2011 at 11:01pm
priya wrote:

hello sir
i want to charge a 1.5v cells used in dc pumps
by switching it to main supply

On October 24, 2011 at 1:15am
zz wrote:

probably 4.2V, but it is also limited in current.
you misunderstood the question jin

On October 25, 2011 at 7:27pm
Postelle wrote:

Wow,  jin is really smart?  Maybe she should be the one writing the articles!

On October 28, 2011 at 9:52am
Ed wrote:

I have a Toshiba C655-S5056 laptop with li-ion battery.  Specs say 6 cells, 48Wh.  The AC adapter is 65W (19V, 3.42 A).  The laptop is dead and I want to manually charge the battery to determine if the problem is the dc jack. 

Can I remove the battery and connect it directly to the adapter for an hour to partially charge the battery?  I know it’s not safe to leave it connected.  I just want to charge it enough to power up the laptop for a few minutes before I go to the trouble of replacing the dc jack.

Thank you.

On October 29, 2011 at 1:51am
Tony wrote:

I want to use 3 AAA size of these in series in a headphone amplifier. There is no chemical recombination applicable as in NiCd or NiMH, they are more like capacitors in that way. So it seems they can’t be charged in series. It would quickly ruin the lowest capacity one. Is this correct?  Can you suggest some really simple but safe way of charging them, one at a time if necessary, using only a regulated variable power supply with constant current limiting, a good quality analogue multimeter (Avometer) and maybe a resistor? I don’t need anywhere near maximum capacity. Are they easily damaged if the strongest ones reverses the weakest and therefore should be protected with diodes maybe? Can you suggest any good information about using them in series? Sorry, I should be paying you a consultancy fee for this lot!  Thanks.

On November 1, 2011 at 1:45pm
Brian Ahern wrote:

I have an electric car with Lithium ion batteries. I have a data logging voltmeter across the 170 volt series pack.  When I hooked up the meter after stopping the car it took 2 hours for the meter to stop jumping all over the place in its voltage readings. After that it became super stable. What is this agitation you are speaking about?

When the switch is off and the battery pack is opencircuit no electrons can flow. However ion can still flow to equilibrium conditions. Will this look like a slow rise in cell voltage?

On November 14, 2011 at 2:15am
Nitesh wrote:

Dear sir,

I am using the 3.7V/3700mA li-ion battery for my electronic instrument. this battery gets dry after some time. Then i have to remove battery from ckt and directly connect it to the adaptor(4.1v/1500mA). but that is not possible to do all the time.
Please suggest the solution.

On November 26, 2011 at 10:17pm
Niel wrote:

Interesting article. I have just started using li ion, and the charger I have charges to a voltage of 4.10 volts. I have a lot of experience with li po and the charger uses 4.20 volts as the cutoff for that variety. According to the article, I guess that’s a good idea. I just found it a little unusual. Thanks for the info.

On November 30, 2011 at 6:27am
Terry C wrote:

How can I reset my Li ion 14.4 Hilti battery,  peeps say it can be done I only get one single green light and no charge need help on this please,  Thank you

On December 4, 2011 at 1:10am
Twoone wrote:

I am working with an off grid dc motor that requires 48v and 250 ah and i plan for 24 hrs running. I plan to connect to lithium ion battery bank to store energy for later usage. Let say batteries are in series of 4 it means about 12 v. So how many battery shall i have and what is the charger size.? Anybody advise? Tq.

On December 5, 2011 at 11:05pm
voon wrote:

yes i have the same question as ray. my charger specifications are output 5v, 700mA. My battery is 3.7v 1500 mAh li-ion battery… if i want to avoid entering stage 2(saturation charge) region, at what % should i stop charging at? is it 85% which is cut off capacity at 4.2 V/cell, or perhaps somewhere near 60% which is cut off capacity at 3.7 V/cell?

thanks for any help smile

On December 7, 2011 at 8:00am
Ali wrote:

Is it better to charge the Li Pp/Li On faster or slower as I have a variable current charger

On January 1, 2012 at 2:33am
Gary wrote:

I’m having a discussion with someone on a forum.  It’s going like this:

I’ve got 4 7.4v batteries.
2x1000mah + 2x1200mah

I’m parallel charging them at 8.4v, no balancing at this point.

The charger hits 8.4v and cuts off when the current draw drops below a certain point.

My understanding is that each battery will saturate at 8.4v line and no further current will enter a saturated battery.

He’s of the opinion that I’m probably screwing up my batteries.

Anyone have some info?

THanks smile

On January 4, 2012 at 9:22pm
Anand wrote:

Thanks for this wonderful info! really helps

On January 10, 2012 at 4:54am
Asad ali wrote:

what is the equation to find the instant value of charging or discharging of a Li-ion battery ?

On January 25, 2012 at 11:09pm
David wrote:

I have a Lipo battery (11.1V 3 cell / 1100maH) which I have a 12V AC adpator to DC charger with a amp regulator from 0-4 Amps. Firstly can I charge the battery higher than 1100maH or does it have to be lower…secondly it has been on for hours at 1000maH but still it doesn’t charge it? What is wrong? Thank you

On January 29, 2012 at 4:26pm
Vince wrote:

Regarding Figure 1:  Current is listed as being in Amps (A), but is this a typo?  Should it be C, where C is the number of amps that would discharge a cell in one hour?  For example, I have a 3500mAh cell for my Droid phone, so would not C equal 3.5A?  Is 3.5A then the amount I would want to use to initially charge my cell until it’s voltage reaches 4.2V, at which point the cell itself will determine how much current it draws?

The article later states “The charge rate of a typical consumer Li-ion battery is between 0.5 and 1C in Stage 1”.  I would LOVE to have that, but can’t find ANY!  So is this another typo in the opposite direction?  Did they mean between 0.5 and 1A instead of C?  Because that’s the range most charges seem to max out at.

I have one charger that outputs 300ma (which is 0.085C), a few 500ma, and 800ma, and one that does a full 1A, but even that one is only 0.3C.  These take TOO LONG to charge my cells.

To Ryan who posted on May 3, 2011, how’s your project going?  That is my need also.  I will be backpacking for a few weeks with my Droid.  I have four 3500mAh cells, and a 10W solar charger.  If 1C for my cells is 3.5A, at 4.2V that would be 14.7W, so my solar panels will never be able to provide more than the battery should be able to handle.  Right???  The problem is that I can never count on ideal sunlight, so I pretty much want to pump everything the panel can generate straight into the cell.  However, all of my adapters that output 4.2V have severe current restrictions as I mentioned above, so I don’t think I can get a full charge from the sunlight available.  Any advice??? 


On January 31, 2012 at 7:10am
Dobra Georgian Ionut wrote:

I have a Samsung Galaxy s and please tell me if I use my phone while charging the battery is damaging in any way. When charging the phone is using charger electricity or battery electricity ? (the phone has a Li-ion 1500mAh 3,7 V and original charger output 700mA 5V )

P.S. Thank you ?

On January 31, 2012 at 9:02am
Vince wrote:

No, that is not bad, and sometimes is necessary. 

If your draw is less than the charger is putting out, then power from the cord is going both to the phone and the battery.  But if you are drawing more than the cord can supply, then the phone is drawing from both the cord and the battery. 

In extreme cases, the charger may not be able to keep up with the draw from the phone, for example if you are providing a wifi hotspot, recording a HD video with the light on, and geotracking your position simultaneously, all while trying to sling mad birds at swine, your battery may continue to discharge even while plugged in, but that’s the only way to make it last as long as possible.

The battery will charge fastest when phone is turned off because all of the power from the cord can be directed to charging the battery instead of also running the phone, but that is not practical for most people.

Same goes for laptops.

On January 31, 2012 at 9:10am
Vince wrote:

Another clarification that I think should be understood:  The thing that plugs into the wall at one end and your phone at the other end is not really the charger.  The charger is inside the phone.  The wall cord provides 5v to the phone, and the charger inside the phone provides 4.2v to the battery.  Although there are (and I have one) actual chargers, where you take the battery out of the phone and set it in the charger, which plugs into the wall. 

The difference is that a charger is (or should be) smart enough to first supply a conditioning charge, then a constant current, and finally a constant voltage, and preferably a shutoff.  The charger in the phone does this.  The cord from the wall to the phone is not smart, it just provides a constant 5v.

On January 31, 2012 at 9:41am
Dobra Georgian Ionut wrote:

Thank you Vince ! very usefull ; another question :
I have in my android phone a program that tells me much about battery status and tells me that when fully charged is about 4.2 V,  above in this article I saw that charging is recommended under the maximum voltage to extend battery life (which you think that is the maximum voltage that the battery should be charged for above recommendation?) the program shows also battery temperature (which you think is the maximum temperature would have to be?)
If i’m watching a movie , or play some games or surf web is better for battery to keep phone connected or not to charger ?

P.S. Thank you!

On January 31, 2012 at 10:16am
Vince wrote:

From what I’ve learned from these websites, here are the answers:  First to your last question:

What is really best is to keep your battery around half charged, 40%, 3.7v.  So if you’re fully charged, it’s best to unplug it regardless of what you’re doing, and if it drops to less than those numbers, plug it back in.

Two things are bad for the battery:  First, to let it completely discharge, which is almost impossible in normal operation because the phone itself will turn off long before the battery is empty in order to prevent such a thing.  The battery itself also most likely contains a similar monitoring circuit, although at a lower threshold.  Second bad thing is to keep it at a high voltage like 4.2v.

Think of it as you breathing.  In your normal daily routine, you don’t empty your lungs as far as they will go, nor take as deep a breath as you can.  You work best somewhere in the middle.  But if you know you’re going diving underwater, then you’ll want to first fill up with as much oxygen as you can hold, so you can stay under water for as long as possible.  But to live your daily routine that way would be very stressful on your body.

Now in regards to your first question, and with the understanding of the above, no 4.2v is not recommended for extending battery life.  4.2v is a rather arbitrary value that’s been agreed on by the industry as providing a reasonable balance between long term longevity and short term runtime.  If you don’t need to survive all day without access to electricity, you’d be better to stop at maybe 4.0v or even 3.9v.  However, the tradeoff is that you’ll get fewer hours without the charger.

People tend to be less concerned with how many years their battery will last, than how many hours it will last, and will often throw out the whole phone in two years anyway. 

As for temperature, I personally feel that the heat is generated more by the phone than by the battery.  Put a healthy battery in a phone and use it hard for a few hours, and the phone itself will raise the temp of the battery, simply because the battery is inside the phone.

Finally, as for what the phone app reports, it’s mostly guesswork (except for temp and voltage).  But the voltage is not a reliable indicator of remaining charge, because the voltage can stay close to 3.7v most of the time.  The percentage left is guessed by trying to track and count how many amps the phone is drawing from time to time, sampling it maybe every few seconds, and comparing that to the expected capacity of a new healthy stock battery. 

On my phone with an extended battery, the phone will drop to 5%, and then continue to run fine for another day.  So while voltage isn’t real accurate, it’s what I watch and I know that when it falls around 3.4v, it’s approaching empty.  Then again, if you’ve been using it heavy and let it sit, the voltage will come back up a bit.

On February 6, 2012 at 8:30am
David Parkinson wrote:

I have a need to overcharge a Lithium battery until failure.  However, the charger we have limits the current as the voltage is reached.  What kind of a charger will allow me to overcharge a battery?

On February 6, 2012 at 9:50am
Vince wrote:

@David, my understanding is that it’s the battery itself, not the charger, that limits the current once it’s getting full.  With a typical 4.2v charger, once the cell is saturated at 4.2v, it simply won’t draw anything more.  Zero current. 

In order to force more in, you’ll need to increase the voltage.  Maybe you can find a 4.3v charger?  Or just hotwire it to 3 fresh alkalines in series, giving you 4.5v.  I don’t want to be standing anywhere near you when you do this.  When you say “failure”, I assume you mean loud noise, smoke and flames, and lithium shrapnel killing everything around you.  You also could hook it to your car battery.  Any DC source of significant voltage should cause the catastrophic failure you seek.

Legal disclaimer:  Don’t actually do any of this.  In fact, forget that I even wrote it.  These are bad ideas, and nobody but you will be responsible for the consequences. 


On February 6, 2012 at 10:11am
David Parkinson wrote:

Thanks Vince !  You are almost correct on the failure scenario (they do burst into flames, but no real loud noise or shrapnel).  This testing will be performed in a stainless steel tank for the purpose of analyzing the gases that are made through this type of failure.  We have previously induced battery failure through external heating, case crush and internal shorting.  The next method we wanted to cover is the possibility of a failure in the charging mechanism that might allow an overcharging situation.
Regards,  Dave

On February 6, 2012 at 10:23am
Vince wrote:

@David, ah, glad to know you know what you’re doing.  I never know who I’m responding to, so I often lean toward dramatic caution.  grin

But you your goals, a conceivable failure might result from a USB charger somehow shorting the 5v input straight to the intended 4.2v output, resulting in what you’re looking for.  The USB out from wall chargers sometimes can supply over an amp.

On February 8, 2012 at 4:28am
b fvb wrote:

yeah men

On February 8, 2012 at 4:30am
Sexama wrote:


On February 15, 2012 at 2:38am
Marios Michaelides wrote:

Just bought a Li Ion receiver battery pack and the istructions say i should plug the balacing plug in the charger, as well. The pack only comes with one plug, the one the plugs into the receiver. So how is it possible to balance the cells?

On February 16, 2012 at 4:25am
Juan wrote:


I have a question that I have not fully satisfied by reading this website.

Using a laptop in a continuosly way, is it better to fully charge the battery and then to fully discharge it or is it better to have the charger always connected?

On February 16, 2012 at 10:19am
Vince wrote:

@Juan, the question to your question is “is it better for what?”  Better for the longest long-term life of the battery?  Better for the longest runtime the next time you need it? 

In any case, the worst thing to do is to use it if you don’t need to, to run the laptop off the battery when there is AC available.  1.) Batteries will last for a few hundred charging cycles.  Fully discharging them and recharging uses those cycles.  2.) If you suddenly need to hit the road, you will only have a partial charge.

The best thing to do for the longest runtime when you need it is to keep it fully charged.  However, this will reduce the long-term life expectancy of the battery.

The best thing to do for the long-term life of the battery would be to charge it to 50%, take it out of the laptop and don’t use it, and just run the laptop on AC.  Recheck it every few months to keep the charge around 50%.  If you are planning a trip, then put it in and top it off before you go.  But this all seems a little inconvenient.

So the bottom line is that you’ll have to choose a balance between long-term, short-term, and convenience, based on your own personal goals.

On February 16, 2012 at 2:16pm
Juan wrote:

Well Vince, thank you for your reply.

My question was….better for longest long-term life of the battery.

I mean if you have to work with battery on because you need to move in the office you cannot put and take off the battery every time.

I read about someone that think it is better to charge the battery and then take off the charger to let the battery discharge and then re-connect the charger and more over!

Instead some other one assure that is better to leave the charger always connected to also get the battery always balanced…

I don’t know…you reply is quite clear and I know the better way is to not use the battery but I’d like to know your reply in this scenario.

Thank you.

On February 16, 2012 at 3:58pm
Vince wrote:

@Juan, yes, in your case I recommend plugging it in whenever convenient.  There is no advantage to unplugging it for the purpose of intentionally discharging the battery.  That only hurts it.

Remember that the power cord is not the charger.  The charger is inside the computer, and it will stop charging the battery when the battery is full, even when the power cord is still connected.  At that point the computer is running AC, not the battery, and it will take a long time before the battery drops low enough on it’s own for the charger kick back in again.  But when that happens it will quickly top off the battery again, and you probably will never notice it switching.  So the battery will always be kept very close to full, so it’s ready when you do need to use it.

On February 17, 2012 at 12:54am
Juan wrote:

@Vince: thanks for your answer. I know the charger circuit is in the laptop…It’s just the name we usually give to it.

Your answer let me get a question too: If the charger stops to charge the battery and the computer will run AC for a while, why in the article is mentioned that the battery can reduce its life because to some chemical effects.

What do you say about this aspect?

Thank you very much

On February 17, 2012 at 7:00am
Vince wrote:

@Juan, I’m not sure I understand your question correctly, but if I do, this is my answer:

Keeping the battery at full capacity does reduce it’s life because of the internal chemical stresses it suffers at high capacity.  But this is how most chargers are designed.  This is the tradeoff, the downside to being prepared for maximum run-time.

Batteries are most comfortable at half capacity.  This is why I say it would be best to charge to 50% and then remove the battery if you know you won’t be needing it for a long time, because the chargers are not designed to stop and leave it at 50%.

On February 19, 2012 at 3:30pm
Juan wrote:

Well the question was a little different but that’s ok about your answer.

Thank you very much.

Bye bye.

On February 21, 2012 at 3:12pm
Sapan wrote:

How does this apply to an iPhone? If I want to maximize the life of the battery should I charge approximately to 75% then let it drop to 25% and then keep repeating?

On February 21, 2012 at 3:13pm
Sapan wrote:

And why does apple recommend draining your battery completely at least once a month? http://www.apple.com/batteries/iphone.html

On February 22, 2012 at 9:38am
Vince wrote:

@Sapan, I’m sure the info on this site would apply to all Lithium-Ion cells, including those used by an iphone. 

Yes, your 75% to 25% sounds good, trying to keep it around half way.

Their recommendation to completely drain it monthly makes no sense for getting the most out of the battery, but it may be useful for calibrating the phone.

Over their lifetime, the maximum useable capacity slowly decreases.  By periodically topping it off and letting it run down to where it turns itself off, your phone can learn what the new capacity is, and thereby giving you a more accurate percentage remaining indicator. 

Phones have no way of knowing or measuring how much charge is really left, because the only measurable value of the battery is voltage, and as you can see from the charts at the top of this page, the voltage can stay around 3.7v for a very long time and then drop to dead very suddenly.  So what they try to do is keep a running total of how many milliamps were drawn over frequent small intervals.  It’s kind of like a printer trying to estimate how much ink is left based on how many pages you’ve printed since installing the new cartridge.  Not real accurate, but it’s the best it can do.

So by topping it off and then running it to completely dead while the phone counts how much it’s using every second, it can get a pretty good idea what the total expected capacity should be, and use that info to calculate a percentage remaining.

On February 22, 2012 at 2:14pm
Georgian Dobra wrote:

Did someone now some tips for charging unused and new li-ion batteryes ?
I recently bought a new 3,7V ,1650mAh samsung battery for mai GALAXY S ,  I’ll wait your answer before first battery use.
Also the old battery (1500mAh) it’s in a good condition (not even 30 charge cycles)
, do you have some advices for preserving and alternative use uith the new one ?


On February 22, 2012 at 9:26pm
Vince wrote:

@Georgian Dobra, Advice:  charge it and use it.

I recommend an external slow charger.  I just ordered another from ebay for under $3.  Initially charge new battery for 12 hours.  Then each morning, simply swap the freshly charged battery into the phone, and place the other battery into the charger.  Repeat each morning, and you may find yourself free from charging cables!  grin

Slow charging over night provides a deeper, more saturated charge, by skipping stage 1 (as depicted in the initial graph on this page) and going straight to stage 2.  Admittedly, charging this fully is not optimal for long-term longevity, but gives the best run-time without overcharging.

On February 23, 2012 at 10:29am
Dobra Georgian Ionut wrote:

thank’s Vince for your fast answer !
unfortunately I am from Romania (East of Europe) and I don’t have ebay . Ofcourse there are some alternatives foe ebay in my country but those are much expensive then ebay. Even so I might find this kind of charger but which is the optimal amps when you say slow charger (also as an alternative I can use a normal wall charger used for a bluetooth headset <550mA , 4,75 V> ; is this a good idea ?)
some advices for my actual circumstances ?
Yet I am counting on using larger capacity battery and the oldest only in rare cases…

thank you again !

On February 23, 2012 at 11:24am
Vince wrote:

@Dobra Georgian Ionut, No, 4.75V is not a good idea.  Too high.  Besides, how could you connect that to your battery?

The charger of which I speak accepts the battery directly.  The manufacturer’s website is www.yiboyuan.net.  Everything there is in Chinese, but you can see pictures.

My charger came with a 3500mAh battery.  In my case, the C value is 3500mA, the amperage at which a full battery would be drained in one hour.  My charger output is 350mA at 4.2V, which is 0.1C for my battery.  This is slow, and it takes about 12 hours for a full charge from dead.

If you can see this website, it is a picture:  http://ecx.images-amazon.com/images/I/41JPn8azc4L._SL500_AA300_.jpg

On March 10, 2012 at 1:38pm
CXR wrote:

Hi Vince,

I’ve been reading some blogs on your site. Super informative!!
I have some questions of my own RE Li ion EV batteries. I have done my research & believe I understand to be true, Li ion EV batts like to be kept at a 50-85% state of charge (SOC). If this is true then I also believe to be true the Li ion EV batt will last quite a long time.
1. Is a trickle charge an appropriate way to keep the Li ion EV batt at the nominal 50-85% SOC?
2. Is 4.20V DC the nominal voltage to make this happen or is it better to use a 4.00V DC or lower?
3. Can this be managed , i.e., with the old 1960-65 generator and voltage regulator automotive setup where the ICE auto-engine ran a generator and a regulator was used to keep the battery charged to optimum volts/amps, i.e. only?
4. What voltage/amperage would be best to provide to a Li ion EV batt to keep it at this 50-85% SOC, happy area , if the EV batt is using 4.2V cells, as many as 6000?
Thanks in advance for responding,

On March 10, 2012 at 5:33pm
Vince wrote:

@CXR, Thanks for the positive feedback.  Unfortunately, your questions are beyond my area of knowledge.  I even had to look up what “EV” meant!  grin

I hesitate to discuss things if I don’t know what I’m talking about, but if I may speculate and extrapolate what I’ve learned, and apply it what I’m guessing an EV might be, that being just a large battery of Li-Ion cells… 

1.  I don’t believe there’s such a things as “trickle charge” regarding Li-Ion cells.  You simply set the voltage, and the cells draw what they can.  As they become saturated at that voltage, they just won’t draw any more current.

2.  4.2v is generally considered to be 100% capacity.  3.7v would be 50%, the “nominal” voltage.  Because it’s not a linear transition, I think your 85% goal might even be achieved at 3.9V.  I’m just guessing based on discharge charts I’ve seen.

3.  You’re over my head.  wink

4.  I don’t think there’s such a thing as a 4.2V Li-Ion cell.  The current norm is 3.7V (nominal) for cell phones, which have a non-linear runtime voltage between 4.2 and 3.2V.  As for your maximum current, you’ll need to do a little math.  First you need to know the capacity of each cell in mAh, then multiply by the number of cells in your battery.  For example if I were to use four cells each rated at 3500 mAh, I’d have C=14A, the current at which the battery pack would be depleted from full to empty in one hour.  Next you need to know the manufacturer’s maximum recommended charging rate.  If it’s 0.5C, then I’d want to charge at no more than 7A.

Now that’s all assuming that your battery pack is wired in parallel, which is probably not the case.  If your 6000 cells were 600 parallel packs of 10 each in series, then your 3.7V nominal becomes 37V. 

Bottom line is that I’m not qualified to answer your question.  Your specifics will depend on many variables I’m not familiar with.  However, my guess would be that by charging 6000 cells from a household outlet, you’ll probably never come close to the maximum charging current.

On March 11, 2012 at 6:25pm
CXR wrote:

Thanks for getting back so quick. I’ll make an attempt to simplify.
1. An EV = Electric Vehicle.
2. Trickle charge is generally not regarding Li ion batteries, yet, if you would humor me,
RE “set the voltage” , If the voltage is set at 4.2v - 3.7v and stays constant for 6-8 hours
intermittently will this charge the battery, if the battery is first fully charged ? .By intermittent I mean 3 hour at 4.2v , 3 hour at 3.7v , 1 hour at 4.2v.
3. RE “Over your head” the scenario in # 2. above, is what I am describing. Just trying to understand if I can , or need to start or stop the charge automatically. (Voltage Regulator)?
4. I am not speaking about a cell phone or a small battery. Please think EV.
Manufacturer recommended charge rate is not what I am thinking. I am thinking if I can keep the Li ion battery charged with a trickle after an initial full charge
5. I will hunt down the ,” 6000 cells in parallel or series and /or bundled” and see if I can find this info to give you a more intelligent basis to answer.

On March 11, 2012 at 6:44pm
CXR wrote:

Just found the info on parallel/series.
For the Li ion batt I am speaking about a full re-charge requires 3,5 hours at 70 amps, 240 volts.
This battery when fully charged stores approx. 53 kWh at a nominal 375 volts.
I think this may help you   and   I   with the calks you are trying to teach me.

On March 11, 2012 at 6:54pm
CXR wrote:

I left out some important info.
6000 cells are arranged into 11 sheets connected in series. Each sheet contains 9 bricks connected in series. Each brick contains 69 cells connected in parallel.
Cells are the 18650 type found in laptops.

On March 11, 2012 at 9:58pm
CXR wrote:

What is meant by “the absence of trickle or float charge at full charge”  RE a Li ion battery.
This comment is from the Battery university article “Charging lithium ion “
Does it mean that a Li ion batt can use a trickle charge when it is not at full charge?
Does it mean that a Li ion batt cannot use a trickle charge at all , anytime?
Thanks CXR

On March 11, 2012 at 10:23pm
CXR wrote:

Vince ,
I think I may have found my answer. please see same article as above Charging lithium ion
Section 1 paragraph 17 second to last sentence, “Charge absorption is very high and with a low and intermittent charge ,charging simply takes a little longer without negatively affecting the battery.  The absence of trickle charge further simplifies the charger.”
1. What is a low and intermittent charge ? below 4.2V ?
2. What is meant by “the absence of a trickle charge?’
3. Can I put , what I call a trickle charge,  of 3.7DC-4.2DC without harm to the battery in a
“low and intermittent charge” format?

On March 12, 2012 at 11:08am
Vince wrote:

@CXR, thanks for the clarifications.  The sum of my knowledge about electric vehicle batteries is from what I just learned from you. 

So if you’re talking about a battery consisting of thousands of cells, and the battery has a nominal voltage a hundred times higher than that of any cell, I can’t imagine what you’re considering using 3.7-4.2v for.

Since the battery is nominally 375V, and it takes 240V to charge it, then the 240V (I assume AC) is powering a dedicated charger, not charging the battery itself.

If we just scale the numbers from a normal Li-Ion cell up by a hundred fold, simply as a thought experiment, maybe your 85% goal would be achieved at four hundred volts DC.  Once the battery pack is saturated at that voltage, the charging current would be zero.  But all batteries have some self-discharge, plus Li-Ion usually have some monitoring circuitry, so your real “trickle” current would probably be equal to whatever the total self discharge current would be.

THOUGHT EXPERIMENT ONLY!  The info I provide should only be used for thinking about things, not actually doing anything at all. 

On March 12, 2012 at 11:13pm
CXR wrote:

Thanks Vince for your help !! 
i’ll be back at you in the future, i am sure.

PS don’t be a stranger , if you find something you feel may help me send me an email !

On March 30, 2012 at 10:38am
Blake Cooper wrote:

As always, a wonderful post, full of great information that would otherwise not be readily available. I’m sure I’m not alone in saying that Battery University has been a great help in my professional and hobby lives!

On April 4, 2012 at 5:00pm
Hanyu Liu wrote:

I feel so lucky in reading this article.And I’m interesting in the charging methods used in USA,Germany and other developed countrys. If you are convenient,please tell me the research status about some developed countrys.Thank you ! Thank you !Thank you !
      Thank you ! Thank you !  Thank you ! Thank you ! Thank you !

On April 13, 2012 at 4:07pm
Damian wrote:

just bought a brand new MOTOROLA RAZR XT910. It has an (incorporate) Standard battery, Li-Ion 1780 mAh.
For the best performace how should I do the first charge? Phone turned off and 12 H of charging? Do I need to repeat this the 2nd and 3rd time?
Many thanks!

On April 22, 2012 at 2:54pm
Christophoros wrote:


I disconnected the old 11.1dc Li-ion laptop battery and remove all the 6 cells from it (Note:i removed when the battery was discharge)

I have connect 3 in series (i get 10.5VDC) and also the other 3 in series (i get also 10.5VDC) and finally the 2 packs in parallel for longer runs.

So 10.5+10.5 in paraller=10.5VDC

The question….How do i charge them? What transformer shall i put?

On April 25, 2012 at 6:18pm
Ace wrote:


I have an application where I’ll be using Lithium Ion Phosphate batteries in the Antarctica in -40 deg C temperatures.  Normal charger voltage is 3.65V per cell.  Would I have to increase this CV?? if yes then by how much.

On May 2, 2012 at 7:01pm
wazzink wrote:

i salvaged a laptop battery and got a lithium-ion battery pack and i threw away the circuit before i did my evil laugh..
now i got 3 pairs of parallel 18650 batt connected in series with 10.8v nominal and rated 3.2AH.. when fully charged reaches 12.6v
i hope you can imagine the config. well it looks like this |=|=|=|
my questions are:
1. Can i use a charger with 12v and 1.5A max to charge the whole pack??
2. What if i use a max 1A?? max 500mA??
3. Does the charging current automatically drops as the batt pack reaches 12v??
4. I’m planning to use LM317T or LM7812 for the charger and charge the pack for max 3 hours.. is it ok??

On May 2, 2012 at 7:20pm
Vince wrote:


1:  probably
2:  slower, better charges
3:  yes.  Current flows from higher voltage to lower voltage, like from a tall bucket into a shorter bucket.  Once they are the same voltage, current flow will stop, or reduce to the rate of parasitic self discharge.  Essentially, trickle charge.
4.  don’t know about model numbers, but since 12v is less than 12.6v max, I would think it should be safe to leave it hooked up there indefinitely.

One word of advice:  I’ve read warnings against building your own battery packs, because all cells must be balanced, or one will discharge faster, go negative, and then bad things start to happen.  But in theory, yes I think it should work like you plan.

On May 2, 2012 at 8:13pm
wazzink wrote:

thanks man!!! got a fast reply, i thought i’ll be checking this site next week.. thanks
i didnt touch the connection of the batteries, already in that setup when i took it out from the batt pack.. only i threw away the protection circuit..
the brand is panasonic CGR18650HM.. is it good one??
what should be the final charging current before i disconnect it from charger??
LM317T and LM7812 are voltage regulator ICs with max out current of about 1.5A..
thumbs up to you dude

On May 2, 2012 at 10:07pm
Vince wrote:

Sorry, can’t tell you if panasonic CGR18650HM is good.  No idea.

Regarding final charging current:  The value referred to as “C” is the current at which the battery would fully deplete in one hour.  In your case, C=3.2A.  According to the first chart at the top of the page, batteries can be considered full when the charging current falls to 3% of C, or about 0.1A in your case.

On May 3, 2012 at 3:44am
wazzink wrote:

thanks Vince!!!
I’m so lucky i found this site first before i can make a bomb..
i think i’ll cut it off in 200mA for more safety..
thanks dude..
i found 2 devices attached on one side of the batt pack which i didnt remove..
one is,i think, for temperature sensing,..and the other one connected in series in +terminal and i dont know to what use it is but i dont wanna take it off.. i am thinking if the second part has something to do with current limiting so im planning to keep it there..
i googled the part no. 4MM80H1-19 but no info found..
SALUTE to you man!! very big help..

On May 3, 2012 at 9:12am
Vince wrote:

grin  Glad I can help.  I don’t think you need to worry about safety at the ending current.  Since you’re only charging at 12V instead of 12.6V (divided by 3 would be 4v vs 4.2v, where 4.2 would be considered “full”), you’re never charging to full capacity anyway.  Slower charging is better than faster.  The voltage is the safety issue, and 12v will be great for safety and also longevity of the battery.  I think the cutoff at 3% is more simply because there wouldn’t be much advantage to keeping it charging beyond that, as it’s already just about saturated.  My chargers only charge at 350ma max, and yeah, they take all day.

On May 9, 2012 at 5:25am
Walter Baeck wrote:

Wonderful site ! Thanks for this very clear explanation.

On May 25, 2012 at 2:38am
maksud wrote:

I have one question that if i give 12Vdc charging to 6Vdc Li-ion battery directly then what will happen to battery? which effect may be seen? . If something happend to battery then I need some mathematical prove. thanx. I need answer urgently

On May 29, 2012 at 8:51am
Mar wrote:

Some clarification please
1) How could an over-discharged single 3.7v Li-ion battery be “boosted” to life again? Having this is battery specs ( US18650gr )
Nominal Voltage               Average 3.7 V
Nominal Capacity             2200mAh,  Minimum 2150mAh
Max. Charging current       2.2A Max.
Max. Discharging current     4.3 A max.

2) Could I use the basic 5Vdc /800ma Nokia cellphone charger without any modification for boosting?

3)  Is it better if the voltage is lower than 4.2V dc for safety and other concern?

On May 30, 2012 at 6:53am
Ron wrote:

Hi Mar,

#1. Depending on the battery some will have a tiny plastic label covering a set of electrical contacts that must first be briefly shorted with something such as a paper clip. This resets the electronic safety device installed in the battery itself. From there you should check the voltage on the battery before charging it. If it reads 1.6 volts DC or less then toss it in the garbage simply due to the fact that the battery may be unstable from this point on. Other than that placing it on a charger and checking the voltage after a few minutes to see that it is charging is a good idea.
#2 I am unfamiliar with those chargers
#3 At 4.2 volts you do get a greater amount of charge into your battery than at a lower charge voltage, the only risks are to battery life expectancy due to the fact that your battery is approaching it’s maximum safe voltage point (4.3v is really bad), but then again temperature, rate of charge, and the average charge state of your battery would also be factors that would diminish your battery’s life expectancy. So going to only 4.0vdc on a charge but doing it on a fast charge and keeping your battery on full charge for vast amounts of time would be worse for the battery life expectancy than a modest amperage 4.2 volt charge rate.

On June 1, 2012 at 1:14am
Richard wrote:


I have a 24V 10Ah Li-ion battery that I want to charge whilst on a boat. I have no details about the boat as we are unsure what boat we will be using.

My questions are

1   How much current would the bike take when charging?

(I need to knowthis so that i know we are not draining the boats power when not hooked up to the shore power)

2   What size inverter would be needed?

If you can reply as soon as possible that would be fantastic.

Many Thanks


On June 1, 2012 at 12:36pm
Pantaz wrote:

1. Are any chargers able to determine “C” for individual cells? (So that they can adjust charging rate for different capacities.) Is it even possible, in any practical way?

2. I’m building bicycle LED headlights, and I want to experiment with different cell combinations and capacities in series/parallel configurations. When charging a parallel battery pack, should/can the charge current be increased proportionally? (E.g., “C” for two 2200/mAh cell in parallel = 4.4A, so a C/10 rate would be 440 milliamps?)

On June 1, 2012 at 2:37pm
Vince wrote:


I can only assume certain things based on your question.  You mention a bike?  Maybe you have a rechargeable electric bike?  For your answers, I would look at the charger that came with it.  It should list the current it will draw.  You mention inverter, so I assume your bike charger runs on 120V AC, and your boat has 12V DC like a car?  If this is the case, then you are trying to convert 12V DC into 120V AC which probably has an adapter to convert it back to DC, probably 24V DC.  You may want to see if you can find, possibly from the manufacturer or elsewhere, a different type of adapter.  Also, assuming a boat is like a car, there are fuses that may limit your charging current anyway.

On June 1, 2012 at 2:46pm
Vince wrote:


1.)  I don’t know how a charger could be able to know the capacity of the battery, unless it is perhaps a conditioning charger that fully discharges, fully charges, and fully discharges again to measure it.  Since this is not necessary for Li-Ion, I haven’t seen any that do this, like they used to do for NIMH and NICD.  However, That is exactly the process some people recommend for cell phones to calibrate the battery monitoring software.  As far as I know, that information is only used to display the % remaining symbol.

2.)  Yes, that sounds correct.

On June 9, 2012 at 7:02am
Enrico IK5DFD wrote:

For reduce output voltage of little charger I can suggest to put in series a silicon diode for a voltage drop of approx. 0,7 V (1 N 4401-7) a german diode( more rare) for drop approx 0.4 V.

On July 3, 2012 at 12:35pm
A-Freak wrote:

Hello to the Battery Experts

I want to build some kind of portable “Power Block” where an solar paneel keeps some paralell connected Li-Ion cells (at least 10Ah) charged. It should deliver approximately 100mAh for some LEDs every night and as much capacity as possible when needed a few times per year.

Most important is the longest possible life with respect to remaining capacity. It needs to be available for at least 5 years without service, better 10 or more.

It is clear to me that i loose capacity but gain lifetime when i charge an Li-Ion cell to less than 4,2V so i would like to do this. Additionally charging current would be very slow, at least two sunny days for recharge and much more without sunshine.

Now my question is:
Do i still need some kind of charge termination for this application or would the cells stay happy when i just recharge them up to maybe 3,9V and keep them floating there?

On July 3, 2012 at 6:59pm
jacky wrote:

I own a Htc Sensation XE,
So as u said that 4.2V to charge the battery,
But why the original htc charger output was 5V___1A ???
Since i saw the article said the battery cannot charge more than 4.2V.

On July 4, 2012 at 7:36am
Vince wrote:


It’s my understanding that current can only from from higher voltage to lower voltage, so if your charging voltage is 3.9V, current flow will simply stop until your battery pack drops below the charging voltage.  Therefore, no, I don’t see any need for any type of charge termination.

If your battery voltage goes above the charging voltage, then current could reverse, backfeed into the charger, and drain the battery pack.  This could happen in two situations:  1) it’s cloudy or night time, and the charging voltage drops below the battery voltage, and 2) battery voltage can raise and lower with environmental conditions.  I recently noticed this with my own cells which were left outdoors, not attached to a charger or anything.

On July 4, 2012 at 7:48am
Vince wrote:


Good question.  This is a common misconception because even many of those who know better still use in the common, rather than the correct, way.

The 5V 1A thing you are referring to is not the charger.  It is the thing that provides power to the charger.  The true charger is built into the phone.  The thing you see is just providing high current USB type power to the charger.  It’s quite generic, and can be used to power anything that takes 5V, up to 1A, including USB powered coffee cup warmers, etc.  The charger in the phone, on the other hand, while being powered by 5V and drawing up to 1A, most likely has monitoring circuitry, shutoff, and other smart sensing stuff.  It needs 5V to run itself and to output 4.2V.  The 5V power source has none of that.

On July 5, 2012 at 6:30am
jacky wrote:


Thank for the reply,
This is the great information. I think u can make write this statement to your website, so everyone can read 1 more useful information about the USB adapter charger and inside the phone charger. wink
Thank you.

On July 6, 2012 at 1:30am
manoj wrote:

i want battery for instant of power charging and when the circuit switch is closed it will provide continuous supply and the range is around 12 v

On July 12, 2012 at 7:42am
crs wrote:

I have a razor with a Li battery.  Its wall charger is rated at 4.2v 600ma, but I’d like to build an adapter so that I can charge it from USB (5V +/- 5%).  Could this be done by adding one or more diodes to drop the USB voltage down to 4.2V?

On July 12, 2012 at 9:09am
Vince wrote:

@crs, I think it’s more complicated then that.  Here are some ideas (which are above my head):

On July 16, 2012 at 10:17pm
krist0ph3r wrote:

props to you. excellent article. exactly what i’ve been looking for, for years!

On July 17, 2012 at 1:27pm
Sally ahmed wrote:


I am trying to fabricate Lithium ion batteries but I am not getting the voltage it should reach
Materials are (LiCoO2 Cathode, LiPON solid electrolyte and Ni as the anode)
Theoretically speaking, the voltage should reach 4 or 3.9 V but in my case, it doesn’t go beyond 1.5 “saturates there”, then it gets self-discharged in few minutes

Do you have any idea why i am not getting the 4 V?

Thanks alot

On August 1, 2012 at 6:16am
Kingsley wrote:

thanks guys. there’s an unfathomable wealth of knowledge from this resource. keep it up @ Isidor

On August 7, 2012 at 9:46am
Michael Bernardo wrote:

Thank you for the article! This clears up a lot of the myths going around.

On August 9, 2012 at 6:49pm
Terry Wolbert wrote:

Anyone had experience with a “cell” reversing it’s polarity/ ; and how to get it ‘reversed” ?

On August 22, 2012 at 6:38am
kamal wrote:

i want to learn about battery

On August 22, 2012 at 7:53am
Dan wrote:

Hi All

I noticed above this statement:

“If the discharge continues to about 2.70V/cell or lower, the battery’s protection circuit puts the battery into a sleep mode. This renders the pack unserviceable and a recharge with most chargers is not possible. To prevent a battery from falling asleep, apply a partial charge before a long storage period.”

I have found this to be the case in a system I am designing, as the battery protection circuit releases the battery from sleep mode when a certain voltage is presented across the protected battery terminals, and since my charger IC uses current, it will not cause the protection IC to release the battery from sleep mode.

My question is, how do prevent the battery from going into sleep mode in my system, I have a circuit that shuts off all of the circuitry at about 2.9V and then the system current reduces to about 6 microamps, but over time, this small draw will eventually lower the battery voltage to a point where the battery charger will not be able to bring the battery out of sleep.

How do I handle this in my product?  Is there a special kind of charger IC that will cause the protection circuit to release the battery, or do i simply have to tell my end users not to leave their system uncharged for extended periods of time?

Thanks so much,

On August 22, 2012 at 9:29am
Vince wrote:

Hi Dan,

I think even with a totally disconnected battery, the battery’s own internal circuitry will eventually self discharge it into the “sleep” mode.  I think a cell would have a shelf life for a “long” time, but not indefinite, so no user should ever leave anything uncharged for extended periods.  I don’t see any way around that.


On August 22, 2012 at 9:37am
Dan wrote:

Thanks Vince,

I was leaning toward that possibility after reading numerous articles and such as well.

Does anyone know how to calculate the amount of time it would take a battery to discharge from a particular voltage to a different voltage.  Say discharge from 3.00V to 2.55V with a known current draw, for example 6 microamps?  or at lease a decent estimate?


On August 23, 2012 at 9:54am
Vince wrote:

No, I don’t think so.  The problem is that lithium ion cell voltage doesn’t drop in a linear fashion.  This is actually it’s strength, that it can maintain close to its nominal voltage throughout most of its discharge cycle.  Because of this, we can’t really estimate how much charge remains, based on a voltage reading.  My only experience is with my cell phone, but it estimates remaining charge by trying to tally up, second by second, how much charge it has used, and then subtract that from the assumed maximum capacity.

On September 4, 2012 at 11:51am
Alex wrote:

I have a bike light battery which is labelled ‘Rechargable li-ion 7.4v’. I have lost the charger but I have an AC adaptor labelled ‘PRI: 230v ~ 50hz, SEC: 4.5v - 200ma.
It fits the light battery.
Could I use it to charge the light battery?

On September 4, 2012 at 4:15pm
Vince wrote:

Hi Alex,

No, I don’t think so.  I suspect your 7.4v is actually a battery of two 3.7v cells, 3.7 x 2 = 7.4.
So if a 3.7v charges to 4.2v, a 7.4v would probably need 8.4v.  Just guessing.


On September 5, 2012 at 1:25pm
Alex wrote:


Thanks for your reply. I’ll invest in the correct replacement charger.


On September 10, 2012 at 10:18am
SinthiaV wrote:

@crs @Vince Hi. The way to drop a voltage is to put the circuit in question in series with a resistance. In order to determine what size of resistor to use, you use the series property that the voltage drops across the components in a series circuit add up to the source voltage. Measure the impedance across the outputs of the existing circuit. By applying ohm’s law (v/i=r) you should see 4.2V / .6A = 7ohms this will be r1. The resistor is r2. v1 and v2 are corresponding voltage drops. Since current is equal at all points in a series circuit, we can ignore it and say r1/r2 = v1/v2 for a result of r2=1.3ohms.

There will be a drop in current , however at 1.3ohms I think it will be small. If I remember right (DC theory was a long time ago!) it will be proportional to the size of the resistance.

On September 18, 2012 at 9:09am
nicholas finch wrote:

Some good information on here, well done to all those who have contributed.

I have a very technical question that I am trying to solve.

I am working on an EV Motorbike project, and at the stage where we have selected the batteries, and are trying to make out own charging and Very basic BMS system.

I have 30 x LiFe batteries at 60AH each - wired in series.
We are thinking of placing Relays on each individual cell ( 30 of them ) that will remove the cell from the series, and reconnect the series for the other cells, thus isolating the individual cell when ever an overvoltage or undervoltage level is reached.

For the DC motor operation this is fine - as voltage drops, then max speed drops, and is of no concern to me.

For the Battery charging however, as they are in series, I will need 30 x 4.1V DC = 123 Volts to charge the entire series, and probably something like 10 - 20 Amps. 

As a cell is taken offline when or if it reaches say 4.1 volts. I need to either absorb the
extra 4.2 Volts, or reduce the charge voltage to 118.9 Volts, and so on and so on.

Now… does it make sense to charge them this way?
Is it possible to drop the voltage of a charger from a signal when cells are taken offline?
or would it make sense to add in a resistor to the series to soak up the extra 4.1 volts ( 1 resistor per battery until they are all off? )

Or should I try and make individual charging of each cell using linear voltage regulators such that each cell has it’s own regulator, and if 1 is taken offline, the others should still charge at the same volts ?

Parallel charging is out of the question as this would need massive current. to be normal time… 60 AH cells x 30 = 1800 Amps, so C/100 is still 18 amps, and it would take 100 hours to charge. .... too long!

On September 24, 2012 at 5:11am
Richard Goodman wrote:

I have made up a battery using four 10 AH 3.6 volt LiPo cells. I use these to power a transceiver which requires no more then 15 VDC. All 4 cells in series actually provides 16.8 VDC ... too much for the radio. I have added a switch to bypass one of the cells while the battery has a full charge. This allows me to run the radio at 12.3 volts. When the battery voltage drops, I switch in the bypassed cell. By doing this I am unbalancing the pack by discharging 3 cells more then the remaining bypassed cell. I charge the battery using a smart charger at a rate I limit to no more then 1 amp. I do not monitor each cells voltage individually. If I charge all four cells in series and that one cell is at a slightly higher vol;tage then the others, will they eventually equalize or will there be long term damage?

On September 29, 2012 at 7:58pm

Great questions from both Nicholas Finch and Richard Goodman.  Unfortunately, I say this NOT because I have any answers, but because after reading this entire page, I have very similar questions.  I am building a 72 volt battery pack for my ebike.  I am using 18650 laptop cells.  I have simply removed the 12 cell / 10.8 volt packs from each casing.  I am soldering the leads in parallel and series to achieve a pack with 72 volts (or fully charged at 4.2 volts per cell to 75.6V). Power capacity will be immense and provide crazy riding range while being well within the c rating for such cell chemistry.  As a result of reading this very informative website, I have learned that I would greatly gain cycle life by charging to lower voltage.  I will charge to only 72volts as I can easily sacrifice batt. capacity/range in exchange for a healthier battery.  My question regards cell balancing.  Is a BMS VERY necessary?  If I keep the pack to mid-range capacity use (being conservative in both charge cutoff and discharge cutoff)  can I get away without one?  Will the entire pack balance itself if given time to “rest” after charging to 4.0 volts per cell?  Would such a pack have greater potential for damage if charged to full potential or allowed to drop to a normally acceptable low voltage due to some unbalanced cells dropping too low? AWESOME
SITE!  thank-you.

On September 30, 2012 at 8:11am
nicholas finch wrote:

Hey Mark, I can answer some of your question.

If you want the batteries to last longer, you need to charge with less current at a slower rate. If the voltage of the charger is too high, the batteries overheat and blow up, rather than not lasting a ” reasonable” time.  Your charger should charge at no higher than 75.6 volts, and current should be limited to the Total cell AH current divided by 5 or 6. This will give a 100% charge after 5 or 6 hours.  If you lower the voltage to 72, and charge with more current ( ie your charging the battery faster ) it will not last as many cycles, and also, will not reach full capacity.

If you don’t have a simple bms, the problem arises that one cell will reach full before another has reached full, and vice versa,  The BMS’s normally balance the charge by reading the voltage, and when a battery is reading over 4volts during charging, a resistor is added in parallel to the battery and charger, to reduce the charge on that cell, while charge on other cells catch up. that is how balancing is achieved.

If you diischarge one cell before the others, and go below your cutoff cell, that cell will start getting damaged, and if you go to the extreme, current will flow backwards in it and it will melt, and probably take down other batteries with it.

hope that helps with
some ideas

On September 30, 2012 at 8:15am
nicholas finch wrote:

Sorry, one thing I forgot to add is why the batteries in series get screwed when one battery reaches before the others, it is because current in series flows the same through all of the batteries in series. 

If you were just charging a single battery from empty, and you applied the charger and measured the voltage it would be low, and the current flowing into the battery would be high.  As the voltage in the battery increases ( as it is approaching full ) the current automatically slows down, and when the battery voltage = the charger voltage, there should be zero current flow.  With batteries in series, other batteries that are not full can force current flow through the allready full batteries, which heats them up, and this is what causes the problem.

On September 30, 2012 at 8:44am
Ramhorn wrote:

For my iPhone, what is a good partial discharge percentage before charging?

Second, is it possible to condition li-ion batteries. Say, fully discharging the battery the first time you get your iPhone4, than after that apply the method of never fully discharge before charging. Will this condition the battery, as it is new, to be able take more stress afterwards?

On October 1, 2012 at 10:01pm

Thank-you for your insight Mr. Finch.  I was not aware of the need of a BMS when I started my project.  I have all winter to ponder my options for my Ebike pack here in New England.  I   had not mentioned earlier that my charger is only 4 amps or 8 amps if I use my 2 li-ion chargers to charge two 36 volt packs separately.  The pack will be well over 100 amphours, so charging fully from drained will take a very long time.  It will likely be charging any time it is not being discharged, so this will help.  A rainy day will provide an extra 24 hours of charge for my bike.  I am wondering if the damage( or at least the safety risk) to a cell in series will be minimized by using such a “trickle” charge.  I suppose that if I want to eliminate the risk of causing any one cell from being too stressed, then the current from the charger should not exceed the C rating of any one cell as that cell is acting as a charger for the next cell in series that hasn’t yet reached the full 4 volts that I am asking each cell to accept.  I will likely try to get by with using only one 4 amp charger and adjusting the pots within while measuring voltage with my multimeter to change the charger to 72 volts.
I surmise that not maximizing charge to 4.2 per cell, but rather only 4 volts and only draining to 20 percent will help negate the balancing issue.  I currently plan to only utilize the middle 60% of the pack’s potential.  My riding range will suffer, but that is why I am building such a ridiculously large pack. Range @ ~25mph should approach or exceed 50 miles.  Maybe I should have spent 3 times as much money for a battery from the conversion kit vendor, but then I would only have 20amphours and know very little about lithium ion science.  Tinkering is good fun.

On October 13, 2012 at 4:36pm
Marsman wrote:

I’ve been playing around with some Makita 18v 3Ah Li-ion battery packs. The charger is a fast charger (approx 20minutes) it really pumps current into the packs with short on/off cycles in excess of 10amps. the battery gets quite warm which is not good for Li-ion. As I’m not a “tradie” I use my tools occaisionally and don’t feel such brutal charging is necessary so I’ve investiagted alternative chargers including one that will work from my car battery (Makita sells one for over $150 !!! no thanks!). I found the universal laptop chargers are nearly on the mark, they have selectable voltages and have a 20v setting (one I got was exactly 20.1V and was able to deliver > 5amps). This equates to about 4.02V per cell, very safe even though you only charge to about 80% capacity. It still charges the battery in about 1 hour with current tapering down from about 5 amps to zero).  I don’t intend leaving the batteries connected but at this voltage I presume it would be ok. Interested in experts comments on what I am doing? at about $15 Australian on Ebay it represents a 90% saving on Makita chargers. The battery packs have all sorts of protection in them so I’m not really worried but reading this forum, balanced cell charging might be a concern over time? added advantage is that if the packs have been over discharged the makita charger see’s them as faulty and won’t charge but the Ebay charger doesn’t care (see numerous forums on this topic)

On October 24, 2012 at 11:49am
Paolo wrote:

first of all, thank you for this usefull post!
I’m working on a Li-Ion battery pack 6-cell, 10.8V 5600mAh, coming from my macbook.
The battery is pretty old and has discharged due to inactivity below 9.0 V, causing the protection circuit to switch over. In this state, its charger (magsafe 60W) doesn’t recognize it and it is helpless for me.
For this i’ve decided to try charging it manually. I have a power supply 12V 1.08 A that seems to be suitable, also if it has less power, i said to myself “it’ll employ just 3 times more”: the strange is that there is an intermittent current absorption, normally 150 mA with peak at 1.5 A. Voltage seems to grow according to your graph in stage 1.
Do you think can be acceptable? Or is not good to charge with less power?

On October 29, 2012 at 5:11am
marsman wrote:

they are actually connected 3 series connected sets of 2 in parallel.
you really need to manually charge them carefully, not exceeding about 12.2 volts. most plug pack adapters that say 12v dc are not regulated and will put out over 15v with little load, they will over charge the li ion pack and maybe blow it up if left too long. if you keep measuring the voltage and stop at 12.2 volts you should be ok i think. that should make them look ok to the proper charger but 9v should not be too low you may have a faulty pack

On October 30, 2012 at 4:11am
paolo @marsman wrote:

right marsman,
in fact they went in overvoltage, i’ve used a charge holder for car battery with a resistive load to have the right voltage drop (near 2.5 V) and when the current fell down, the drop had diminished so at the end my barrery was at nearly 13.6 !!! I used a little load to discharge them and now they keep back to 12 V ....

How can i test if they are faulty ? They seems fine for a little load (directly connected), but the mac still refuse to boot ... anyway i’ve ordered a new pack, keeping this one for play ...

thnak you

On October 30, 2012 at 6:17am
idan sl wrote:

For my iPhone, what is better:
1. To charge it all night (8 hours) ?
2. To charge it twice a day half a charge?


On November 2, 2012 at 12:22am
Elliot Craig wrote:

Why are li-ion individual cells only 3.2v?  The reason I ask is for DIY EV applications the cost of the BMS is very expensive, and if the voltage was doubled with the same amps, the cost of BMS would be much less, half the cells to monitor.

On November 2, 2012 at 12:33am
Elliot Craig wrote:

Why are lifepo4 individual cells only nominal voltage 3.2v?  The reason I ask is for DIY EV applications the cost of the BMS is very expensive, if the voltage was double for example with the same amps, the cost of BMS would be much less as only half the cells required.

Many thanks

On November 10, 2012 at 5:39am
Hans wrote:

When you say “Discontinue using charger and/or battery if the battery gets excessively warm”, what is the temperature range you should discontinue charging? I have a new battery in my phone and during charging the battery temperature reaches 43’C.

On November 26, 2012 at 7:26pm
Michael wrote:

thank you very much AWESOME smile

On January 8, 2013 at 6:05pm
Herieza wrote:

Thanks so much for the full mastery and comprehensive article…
much more convincing by your research.

On January 10, 2013 at 5:52pm
Brian Burns wrote:

I have heard some people state that, in terms of power drawn by the charger vs capacity gained in the charged cell, lithium batteries charge most efficiently in Stage 1 and that in Stage 2 the charger uses much more energy to deliver the last bit of capacity to the cell.  Is this true?

On January 15, 2013 at 1:07am

Exellent piece of information, but I have a question. I would like to know if there is a minimum charge of voltage for li-Ion batteries?

On January 20, 2013 at 10:01am
Jack wrote:

I have a smartphone with 2100mAh capacity, I have quite a number different USB chargers, all with the same voltage (5.0v) but different amperage output from 0.5A to 1.5A.  Except my iPad charger (it is rated at 5.1V, 2.1 A output).

I wonder charging my phone with the iPad charger with damage my battery in long term?

I read you reply to nolan above mentioned that we should never charge the battery larger than 1C? I am a bit lost in how to calculate C.  It doesn’t come into the formula or Watt = VI


On January 20, 2013 at 4:10pm
Vince wrote:

Hi Jack,

The 5V and 5.1V things aren’t really chargers.  They are just USB type power sources used for powering the charger.  I mean, you can’t really hook a battery itself up to any of them.  You plug a phone or other device into the 5(5.1)V power source, and the phone itself contains the charger which charges the battery at 4.2V.

The value of C refers to how much current would it take to completely discharge a fully charged battery in one hour.  So C for your smartphone battery is 2100mA, or 2.1A. 

Coincidentally, your ipad “charger” is rated for 2.1A.  But remember that it is not really a charger.  If it were rated for 100A, it would still be okay.  That means that it would be capable of putting out up to 100A of current, but it is the actual charger inside the device that determines how much of that “up to 100A” it would draw, and how much it would send to the battery.  For example, a typical household socket is rated for 15A, but most things you p[lug into it won’t draw anywhere near that amount of current.

Also, the 2.1A * 5.1V power supply is = 10.71 Watts, but the 2.1A “C” value for the battery is at 4.2V, which is 8.82W.  (2.1A * 4.2V)

On January 26, 2013 at 7:03am
Vince wrote:

@Martin, re: minimum charge voltage

Yes, and maybe no.  A smartphone, for example, may have a minimum voltage at which the phone will shut down and won’t come back “on”.  And then the cell itself, or battery, should also have a tiny circuit board, which, as far as I understand, is supposed to prevent it from being drawn down below a different (and lower) minimum voltage, and also to prevent it from being overcharged.  And then there is another point, even lower, below which the cell is truly dead and will not accept a charge.  So each minimum exists to prevent it from reaching the next minimum.

On January 26, 2013 at 7:23am
Vince wrote:

@Martin, more info:

I just found this board, a Protection Circuit Module: 

It’s specs show a maximum of 4.25V and a minimum of 2.5V. 


On January 26, 2013 at 6:00pm
Damon Lee wrote:

I had a new Goki, 3.7v Lithium-ion battery for my cell phone. I charged the battery with the original charger. When I plugged it to the power source and the red light was on the charger and I unplugged it when I saw the light changed to green. Please tell me. Is the battery fully charged? Or should I charged the battery for a certain hours? Please help. Damon Lee ( the old timer)

On January 26, 2013 at 7:59pm
Vince wrote:

@Damon Lee, Not really sure.  I guess it may depend on your charger, and what makes it decide to turn green.  Right now I’m eating a pizza, and soon I’ll decide I’m full.  But after I wait a while and let things settle, I’ll have room again for a little more.

Batteries charging are a lot like me eating pizza.

Fast chargers will feed the battery a lot of charge quicker than it can settle.  They will reach that 4.2V mark in a hurry, but then after you take the battery off the charger, it will go down sooner than if you slow charged it.

Ultimately, if that’s your only charger, then you don’t have a choice.  I assume that once the light turns green, it quits sending out a charge.  So leaving it on the charger won’t accomplish anything if that’s true, nor will it hurt anything.

I think the best way to find out if it is really fully charged is to take it off, leave it off for a few hours, and then put it back on and see if it takes more charge (red instead of green).

On January 28, 2013 at 4:38am
Dave wrote:

Very informative article, although I have a question:

Having charged my LiOn battery, and on the multimeter it shows up as 4.2V, my camera still shows “battery empty” when I switch it on, and would then switch off automatically.

Any idea why?

On January 28, 2013 at 8:51am
Vince wrote:

@Dave, assuming that there’s nothing wrong with the camera itself, this normally indicates that the battery is at the end of its useful life for the camera.  Cameras are high-drain devices, meaning that they require more current than other devices.  The battery may have 4.2V, but can no longer maintain that voltage output at the required amperage.  As soon as a normal load is applied to the battery, it’s voltage drops quickly to a low or unusable point.  But once the load is removed, the battery voltage may measure high again.

It’s also possible that something inside the battery has gone wrong.  In any case, it’s time for a new battery.

On January 28, 2013 at 10:32am
Alan Levi wrote:

According to http://en.wikipedia.org/wiki/Lithium-ion_battery, charge efficiency of Lithium-Ion batteries is typically in the 80% to 90% range.  This is very different from the claim that “Charge efficiency is 97 to 99 percent” in this article.  Can somebody reconcile this difference?

On January 28, 2013 at 10:47am
Vince wrote:

I’m no expert, but I read that to mean charge efficiency is 97 to 99 percent during stage one, when the battery is starting out from near empty and is able to accept nearly all of the energy it’s receiving.  This is when it stays coolest.  Toward the end of the entire charging cycle, even though there is still a slight charging current, the accumulated charge in the cell reaches a maximum and won’t increase.  Therefore, at that point, there is 0% efficiency, all current supplied is being wasted elsewhere.

Efficiency is how much of the energy consumed is being used for the desired purpose.  The rest is wasted as heat.  Electric space heaters, for example, are all 100% efficient because it is their intended purpose to give off heat, so none of the energy they consume is “wasted”.

On January 28, 2013 at 11:07am
Alan Levi wrote:

Vince, understood.  It would be nice to see charge efficiency as a function of time added to Figure 3 (or figure 1).  I wonder what typical threshold values are for various techniques of detecting the cross-over from stage-1 to stage-2. ... and what the techniques are.  If a battery is not used for a significant amount of time (e.g. overnight for a car battery), the charging logic will need to periodically recharge the battery if there’s enough loss.  If this re-top-off is required frequently, then the cross-over period can become quite significant in overall efficiency (energy-in / energy-stored) of charging.

On January 30, 2013 at 11:06am
Phil Fouracre wrote:

Found this site, really interesting.  Can anyone advise me as to how lithium ion batteries on electric bikes actually work.  I have one with eight spring loaded pins for the output connection to the bike and am wondering what do what, does this mean that it has four separate cells, or would some terminals be associated with monitoring or other sensing controls. Am interested so that I can measure and monitor output and performance

On January 30, 2013 at 11:25am
Ben wrote:


I got a question concerning my Lumia 920:
When I use my Lumia, it starts to shut down at about 4% of battery charge. When I then perform a soft reset and start the phone again, I suddendly have more than 20% battery, without charging it. My question is, if this is for safety reasons (so that the battery will never be discharged completly - but 20% seems pretty much), or if this is just a software bug where the correct battery charge is not read out correctly?
Because I really would like to use the 20% too, but if this will demage my battery, I would prefere to charge it.

I hope someone can answer my question.

On January 31, 2013 at 12:44am
Vince wrote:

Ben, no I wouldn’t worry about it damaging your battery.  There’s no way to read how much charge is left.  The voltage is the closest we have, and that’s not real accurate.  When you use the battery, the voltage will drop.  The faster you use it, the faster the voltage drops.  But then if you let it sit, the voltage will increase.  The faster you had been using it, the more you can expect it to increase.  This is because you can draw more current than the battery can provide for long.  Think of it like a bottle of ketchup.  When it gets close to empty, you really have to be patient to get the last few drops out.

On February 4, 2013 at 2:25pm
Bob wrote:

• I’ve read that LIo batteries have 2 stages. 1st staged charges faster than 2nd.  I’ve been monitoring my HTC Inspire phone with a couple of battery widgets that will graph the charge and discharge rates over time.  I’ve been noticing that if the battery is less than 50% and charging, the charge speeds up extremely fast to 100% after it gets to to approx 72%.  The charge graph is not linear but slightly curved until it reaches 70-75% then the battery go to full charge immediately.  I’m doing a test again and currently the battery is at 67%, Battery health is GOOD, temp is 84.2 F, Battery voltage is 4.201V.  I’m using the mfg wall charger that came with the HTC.  Is this normal for the battery to top off like that so fast?  Also when the battery is higher than 80% the charge rate seems to be more linear up to 100%.  Thanks for any thoughts.

On February 6, 2013 at 8:26am
Vince wrote:

@Bob, no, those results do not seem normal to me.  But remember that the amount of charge stored in a cell cannot be measured, so your phone is just guestimating those percentages.  4.2V is normally considered 100% full, meaning that you don’t want to go higher than that.  For it to be 4.2V and still show only 67% charged means you phone is making bad guesses.

Remember that if charged too quickly, it could reach 4.2V without being full.  If you let it sit for a while, that voltage will fall and it will be able to take more charge.  If you charge it slowly enough, it will be more fully saturated at every voltage along the way, and will hold that voltage once off the charger.

Myself, I use extended batteries that my phone wasn’t designed for.  I’ve learned to pretty much ignore the percentage that my phone reports.  I watch the actual voltage instead, again understanding that it does not accurately represent charge, and will fluctuate a lot.  But it’s a better indicator than the guestimated percentage.

On February 11, 2013 at 11:50am
Tony wrote:

I have a Paritrek-S portable nebulizer my wife occasionally uses for asthma. The “power pack” is expensive and two have failed in past ~3 years. I opened one of them and it contains a charging circuit board with components and two Li-io size 18650 cells. What fails is only the cells (18 months and 12 months) . The unit is not used very often and we try to maintain cells charged by “boost” charging every 1 - 3 months or so. It is foolish to spend $120 again when all I need to do is remove (already done) the tabbed batteries and replace them for about $24 or so. Qustion is…I cannot identify if batteries are 1500mAh, 2200mAh, or 2600mAh. They drive a small motor/pump. I am thinking of getting the 2200mAh for about $24 for two. Other than duration for driving the small pump, do you think it will matter on capacity as charger circuit is in tact?  In other words, will impact just be charging time if mAh rating is incorrect? (Cannot determine the LG originals rating)

On February 11, 2013 at 4:37pm
Vince wrote:

Tony, I wouldn’t think changing the capacity should affect anything except runtime and charging time.  In fact, as the cells deteriorate, their capacity goes down anyway.  The rated capacity is the “new” capacity. 

On February 27, 2013 at 8:13pm
Jimi Diga wrote:

Hi Vince,

Would you know the voltage tolerance of the built-in chargers of mobile phones?

My HTC’s plug says 5v—1000maH but I’d like to use a battery pack with a rating of 5.3v—1000maH. Will the .3 voltage difference damage my phone’s battery or lessen its life cycles? Thank you very much in advance!

On February 28, 2013 at 2:08am
Vince wrote:

Hi Jimi,

No, sorry, I wouldn’t.  My phone is a Droid,  which is the only source of my limited experience.  But your question is puzzling, or maybe I don’t understand. 

As far as I know, all lithium cells have a rating of 3.7v nominal (meaning average voltage), with a working range of about 4.2 to 3.2 volts.

A “battery pack” would imply multiple individual cells.  If wired in parallel, they would maintain the same voltage, 4.2 - 3.2.  If wired in series, two cells would produce a battery of 8.4 - 6.4 volts, rated I guess at 7.4.  (That’s 3.7 x 2.)  So I don’t understand where you can get 5.3v from.  ???

Remember that the 5v “plug” is not the charger.  It is the source that provides power to the charger in the phone.  Are you sure the plug says 1000maH, and not just 1000 mA?  mah (milli amp hours) would be a measure of capacity, which would apply to a battery (or “cell”).  ma (milli amps) on the other hand would be a measure of current, which would apply to a power cord, for example.

1000 mah seems like a very small battery for a modern phone.  My batteries are 3500mah.  (At 3.7v nominal.)  The chargers usually get their power from a cord rated at 5V, 1000 ma current.

On March 2, 2013 at 7:05pm
Berno wrote:

how to boosted fairly new sleeping li-ion ultrafire.
thank you

On March 4, 2013 at 2:50am
John wrote:

I’m building a small battery operated radio powered by a 18650 3000mAh (supposedly).
I’m trying to incorporate a built-in charger using a purpose IC - MCP73831 or MCP73837.

I’ve hit the problem of leaving the radio switched on while on charge because, as your article says, the charger may never “see” a current below the termination value and may continue to charge (at Stage 2).

I’m wondering if devices which do allow themselves to be powered while charging (phones, ipads etc)  simply rely on using only enough current to allow the charger current to drop below the threshold or if they use some other method of not “confusing” the charger.


On March 5, 2013 at 4:25am
Chris G wrote:

LiFe 3.3v LiIon 3.6v LiPo 3.7v, there is a difference between lithium ion and lithium polymer batteries. This article suggests there isn’t which is why I mention that there is a difference.

On March 5, 2013 at 5:11am
John wrote:

I found a useful Application Note by Microchip about simultaneously charging a Lithium battery while drawing current from it:

On March 5, 2013 at 10:53pm
Ricky Aspartame wrote:

So would a 5.3v rated after market plug hurt a mobile phone with a packaged 5v rated plug?

On March 6, 2013 at 10:55am
House Mouse wrote:

What can be used to measure the drop in current and switch off the supply of power to a 5v power supply.

On March 6, 2013 at 11:18am
Josh wrote:


From the information presented here and elsewhere, I have divulged that charging at a lower C value is desirable for the long-term health of a li-ion battery.  In my case, I have a cell phone with a non-removable battery, so I am limited to using the built-in charger (& thus cannot slow-charge using an external charger like you mentioned in your comment on Feb 23 2012). Given that my phone came with a 5.1V / 850mA ac adapter, would I be doing my phone a service if I instead used an adapter rated for 5 V / 550mA?  My main concern lies in using an adapter that was not bundled with my phone (though both adapters in question are Motorola branded).

For what it’s worth, I realize I can connect to a PC USB port to charge at ~500mA, but I cannot do this while the phone is turned off (my phone powers on when plugged into a PC USB port)—and this article clearly advises that “A portable device should be turned off while charging.”


On March 6, 2013 at 12:49pm
Vince wrote:

Hi Josh, yes, the adapter you’re talking about would work fine, and would charge it more slowly.  And yes, it’s find to have modern phones on while charging, so using your PC would be perfect.  On my phone, when I plug it in to the PC, the phone gives me some options such as using it as a Mass storage device, or charge only.  I always choose “charge only” unless I want to transfer data from the phone to the pc.

If you use the phone while it’s charging, it will charge more slowly, which is actually a good thing!  If I’m on a long road trip, using GPS and streaming Pandora, I have to keep it plugged in or it will run out of juice.

On March 12, 2013 at 6:34pm
Adam wrote:

I need help! I bought 2 rechargeable li-ion 9v batteries. Brand name is Maximal Power. I need 2 of them hooked up in the 9v clips to give me about 16 volts for led lighting. They will go for about 30 minutes super bright, then one of the batteries cuts off, dimming the lights to almost nothing. Why is it doing this??? I got 2 replacements…. Still not working no matter which of the 4 I use…..

On March 14, 2013 at 11:26pm
SRV wrote:


I am planning to use 2 Li-ion batteries 4.2V and1.5Ah in parallel.
The charge current of individual battery is 750mA.
I am designing a charger circuit for the same configuration.
The charger circuit should be designed for a 1,5A, is my understanding correct?
Can i use a linear charger?
I am wondering how will the charge current be divided among the batteries.
Any information on charging the batteries in parallel combintion will be helpful?

On March 20, 2013 at 5:49am
ken wrote:

my galaxy s3 come with 2100mah standard 3.8v & limit 4.35v
now my issue is that during my idle mode 4.0x~4.1x volt & during charging mode it hit up 4.2x volt.. my temp hit up easily around 39~44ºc
is that meaning my battery lifespan r declined? 9mths old battery only.. how can i undervolt it? really need ur guys assistance. thanks!

On March 20, 2013 at 6:49am
Vince wrote:

Hi Ken, yes, I’m no expert, but I think you’re correct in that fully charging your battery like this will reduce it’s lifespan in order to give you maximum run time.  If that’s not what you want, then you have some options.

First, try charging it from a computer’s USB port instead of a wall charger.  A computer’s USB port is supposed to limit current to 500ma at 5v.  This will give you a slower, cooler, better charge.

Second, while also using the first suggestion, look for an app that alerts you when the phone voltage reaches a certain point, like 4.1v for example, and unplug it at that point.

Third, instead of using the above suggestions, don’t use your phone to charge the battery.  This is the option I use.  I bought a charger on ebay (it was very cheap) and it charges very slowly.  I like this option because I no longer need to plug my phone in.  Very convenient.  Each morning, I just swap the battery with the one that had been sitting on the slow charger all day the previous day and night.

On March 20, 2013 at 7:58am
ken wrote:

@vince thanks for the feedback. open any apps,surfing,video call, & etc less than 5 min it will hit up 38~39ºc
now idle staying at 28ºc/4.06v
if charging with USB i get around 4.1x volt
wall charger >> 4.205v depend on temp. if higher the temp, the higher the volt than can reached 4.274v (max)
ambient temp around 29~32ºc while playing/surfing it will hit up 39~42ºc.
i get restart once due to overheat that reached 45ºc if no mistake.
conclusion, is time for new battery!

On March 20, 2013 at 8:51am
Vince wrote:

Ken, also consider that if you are using the phone to charge the battery, how do you know if the source of the heat is the battery or the phone?  Phones are computers, and after a while there will be a lot of things installed and running that you aren’t aware of.  I see computers that are slow and hot and loud, the fan trying to keep cool the overworked cpu.  Sometimes a reformat and reload works wonders.

Could also just need a new battery like you said.

On March 20, 2013 at 8:58am
ken wrote:

i just guessing cos previously i remember my voltage are fluctuating around 3.8~3.9v
maybe is spyware cos recently i installed lucky patcher. i removed all recently apps doesn’t solve the issue & hard reset my phone it seems slightly better but more or less the same. i think of hardware issue. if lappy fan loud try kill rundll32.exe & avoid open the game explorer at start menu. i bought laptop nearly 3 yrs never reformat. hehe smile

On March 20, 2013 at 9:55am
Tony wrote:

on Feb 11 I posted:I have a Paritrek-S portable nebulizer my wife occasionally uses for asthma. The “power pack” is expensive and two have failed in past ~3 years. I opened one of them and it contains a charging circuit board with components and two Li-io size 18650 cells. What fails is only the cells (18 months and 12 months) . The unit is not used very often and we try to maintain cells charged by “boost” charging every 1 - 3 months or so. It is foolish to spend $120 again when all I need to do is remove (already done) the tabbed batteries and replace them for about $24 or so. Qustion is…I cannot identify if batteries are 1500mAh, 2200mAh, or 2600mAh. They drive a small motor/pump. I am thinking of getting the 2200mAh for about $24 for two. Other than duration for driving the small pump, do you think it will matter on capacity as charger circuit is in tact?  In other words, will impact just be charging time if mAh rating is incorrect? (Cannot determine the LG originals rating)>

Since then, I ordered and installed two 2600mAH cells, as mfr. would not give me “time of day”...they work as good as new!! No overheating, charge time about the same as originals ..  I took a best guess at the LG cells that died and loks like all is great.  “Vince” had replied: “ony, I wouldn’t think changing the capacity should affect anything except runtime and charging time.  In fact, as the cells deteriorate, their capacity goes down anyway.  The rated capacity is the “new” capacity.  ”  looks like Vince is correct!!

On March 20, 2013 at 11:19am
Vince wrote:

Cool!  Thanks for the feedback!

On March 26, 2013 at 12:11pm
Sam Emrys wrote:

@Tony No need to worry it will work fine just the way it is supposed to be…

The capacity has no great impact with the charger circuit unless the charger current is too much high for the new batteries which is possible only if the newly installed battery’s capacity is too much lower then the rated capacity for the charger.  since the charging current in Li-ion battery isn’t much critical factor as compared to Lead acid battery there is no major effect at all except the charging time. Batteries do have internal resistance so the current won’t vary much unless the charging voltage is increased.

let say the internal resistance of battery is 3ohm, voltage suplied is 4.2V
now the theoretical max current drawn by battery will be (ignoring the charge already stored in the battery) = 4.2/3 = 1.4A which will increase only if the voltage increased or if the resistance decreases ( Resistance will decrease upon charging but as the charge increases it will compensate and will reduce the current)

On March 26, 2013 at 12:13pm
Sam Emrys wrote:

@Tony No need to worry it will work fine just the way it is supposed to be…

The capacity has no great impact with the charger circuit unless the charger current is too much high for the new batteries which is possible only if the newly installed battery’s capacity is too much lower then the rated capacity for the charger.  since the charging current in Li-ion battery isn’t much critical factor as compared to Lead acid battery there is no major effect at all except the charging time. Batteries do have internal resistance so the current won’t vary much unless the charging voltage is increased.

let say the internal resistance of battery is 3ohm, voltage suplied is 4.2V
now the theoretical max current drawn by battery will be (ignoring the charge already stored in the battery) = 4.2/3 = 1.4A which will increase only if the voltage increased or if the resistance decreases ( Resistance will decrease upon charging but as the charge increases it will compensate and will reduce the current)

On March 26, 2013 at 12:15pm
Sam Emrys wrote:

@Tony No need to worry it will work fine just the way it is supposed to be…

On March 26, 2013 at 12:21pm
Tony wrote:

Installed weeks ago…works great! Installing same batteries (2nd new set) in the other “power pack” that originally failed. Saved myself almost $100 on each unit as mfr. will not repair and just sells new power packs. Batteries are the only thing that fail and both with tabs are easily replaced once unit is opened.  Mfr. would not reply or give me “time of day” when I requested by phone and email the battery specs. But, had to be one of two or three battery capacities.

On March 27, 2013 at 7:41am
Chris wrote:

Am I damaging my batteries?

I see battery charging voltage and operational voltage in the battery specification.  Battery charging voltage is 3.65V, Operational voltage is 3.3V.  I am charging below this voltage at 3.44V and I see the cell voltages rise quickly initially then slowly up to 3.45 then suddenly to 3.65V when charging shuts off.  Is this healthy for an LiFePO4 battery?  I notice temperature rises of 2 degree Celsius in the pack.  The pack is made up of 16 cells rated at 48V. 

Am I damaging the cells by letting them go up to 3.65V?

On March 27, 2013 at 7:58am
Vince wrote:

Batteries, even rechargeable ones, are disposable items.  Asking if you’re damaging one is like asking if you’re damaging your pencil by using it to write a letter.  Yes, but that’s what it’s meant for.

Current can only flow from a higher voltage source into lower voltage.  So in order to charge a battery, you must charge it with a voltage higher than what it is already at.  If you’re charging your battery at 3.44v, then the battery will never be charged above that.  If the battery eventually reaches a voltage of 3.65, than at least at some point, it was being charged with at least 3.65v.

If you keep everything within the manufacturer’s specifications, it should perform as intended.  The intention is not to make them last the longest, but to get the most use from them.

On March 28, 2013 at 2:03am
JP wrote:

Hi, i have a Li-ion Battery, 3.7V, 700MAh , and i’d like to charge it.
How can i do without the original charger ?

Thank you

On March 28, 2013 at 5:56am
Sam Emrys wrote:


use voltage regulator LM317, see the datasheet, configure it to 4.2V

On March 29, 2013 at 9:26am
Vince wrote:

Hi JP, Any lithium ion charger should work fine.  You can either buy one or make one. 

I’ve bought a few really cheap ones, and they all suck really bad except for this one:

If you want to build your own, without starting from scratch, here’s probably the easiest kit:

Have fun!

PS, you could also probably find a stand alone charger built specifically for your particular cell on ebay.

On May 1, 2013 at 6:03am
RJ wrote:


My name is Robert Jones and I am contacting you in reference to Lithium Ion batteries.  I am seeking some safety information for these types of batteries.  I read your article and understand where these batteries is subject to overheating and can lead to fire and explosion, but I didn’t see anything to prove my case of supplying an eye-wash shower for personnel if they are exposed to the active materials inside of these units.  Also, are there any EPA regulations for these type industrial Lithium Ion batteries?  The internal makeup is made up of oxide and lithiated carbon and I’m wondering if there are any supporting documents that states that an eye-wash shower is required be provided in a Lithium Battery Supply house? 

Make a long story short, we are designing a PV system for grid and we are using/charging industrial Lithium Ion batteries to supply to power to the grid and we couldn’t find any supporting documents that states it’s required to provide an eye wash for such a system is case of contamination.  Your insight will be greatly appreciated. 


On May 1, 2013 at 8:07am
Gabe wrote:

I just built a battery pack to replace one that was worn out. The old pack had six cheap Chinese 3000mAh 18650’S. I bought six Orbtronic 3400mAh batteries for the new pack but the old charger will not charge them. The batteries need to charge simultaneously because they are tab-welded together. Any suggestions?

On May 3, 2013 at 9:00am
Randy Constan wrote:

Well I have a project I’d like to try to actually market involving a transmitter /controller, which seems to run really well for days with just a little single 200maH lipo cell, as it only draws a couple of mA. The project also has a USB connector for its mcu, from which 4.5 volts is available from a pin (there’s a diode in there, hence the missing 1/2V). Well since I’m incorporating a LiPO, I have to consider how it will be recharged, and I’m really trying to keep costs down, so I tried an experiment. I took the 4.5V source, added another diode (down to 4.0V now) in series with a 10 ohm resistor, and tried charging the battery from this arrangement. This amounts to about 80-100mA (1/2C) of charge current for maybe 1/2 minute when the battery is down to 3V, which t quickly drops to a few tens of mA after a few minutes. OK, this is a really slow way to charge the thing, but after about 3-4hours the battery is up to almost 4V, the current is down to a couple of mA, and its ready to power the circuit for a couple more days. Its self limiting because with a 4V source, the current MUST drop to zero long before saturation.

But here’s my question. I realize that with just a few more parts I could use a specialized IC , but my simple diode/resistor combination is cheap and simple. Is there any reason I shouldn’t do it this way? I seriously doubt this would ever pose a safety risk and from the above article,  I gather that at worst I’ll seldom be fully charging the cell. But, then again this could mean more charge cycles, and if the run time from charging this way is acceptable, what is the downside?

On May 3, 2013 at 9:42am
Vince wrote:


I’m no expert, but that sounds perfectly reasonable to me!


On May 10, 2013 at 11:23pm
Ronnie wrote:

I regularly use Li-ion batteries, 650mah and 1300mah. I have two chargers one is 100mah the other 420mah, the former takes up to 6 hours to charge a 650mah battery. Can anyone tel me which is the safest?


On May 10, 2013 at 11:58pm
Vince wrote:

It doesn’t make any sense that a charger would be rated in mah.  That would be like saying a garden hose is rated for seven gallons.  What does that mean?

If all other characteristics are the same, a charger that charges slower is gentler on a battery than one that charges faster.

On May 11, 2013 at 9:52am
Randy Constan wrote:

I agree with Vince, but the way products are marketed these days it doesn’t surprise me one bit that even technical specifications would have incorrect terms. That said, from the explanations on this page I’d say that “1C” is both a typical and safe charge rate, but also that charging at lower rates could give you more charge cycles. “1C” for 650 mAh or 1300 mAh battery would be 650 mA and 1300 mA (not mAh) respectively. So in my opinion, unless you need it charged in a harry the lower charger rate is easier on the batteries. But 100mA for either of these batteries seems excessively low. 

You also might consider getting yourself an inexpensive digital multimeter, if only to find out what current each of these combinations actually are.

On May 29, 2013 at 9:21am
paola wrote:

I have a cell phone battery and 1100mAh 3.7 v, I am using it for an application that is not the phone, my question is, if it is necessary to put an electronic circuit to charge the battery or you only have to let the internal circuit battery voltage will charge it with 5V, how advisable is to do this? ..
thanks for your reply

On May 29, 2013 at 12:32pm
Ronnie wrote:

Of course it makes sense that a charger delivers different mAh. Similarly a 15mm pipe will deliver less water than 22mm hence pipe sizing formula when installing heating systems. I just want to know which is safest!

On May 29, 2013 at 6:03pm
Mario wrote:

Paola, some Li-ion cells have built in over charge protection but I would never rely on that. To be safe, you need to use a charging circuit that would never exceed 4.2V applied to the battery.

Ronnie, you have not specified how your chargers work, however assuming the chargers are designed for Li-ion ie they can handle the initial surge charging current and don’t apply more than 4.2v per Li-ion battery then they are both safe. Use the higher current rated charger. One word of warning- if your battery is faulty (they often short out when faulty) it’s like putting a short circuit across your charger. Good chargers will shut down or current limit but cheap ones may overload and heat up to the point of meltdown. Check your cells are not shorted before charging ie they measure at least 2.5 volts

On May 30, 2013 at 4:02pm
Leon King wrote:

I want to buy a Lithium Iron battery for my motorcycle.  Can I use my old trickle charger which I used on the previous lead-acid battery?

On June 4, 2013 at 10:26pm
Mario wrote:

Leon, definitely no. Read the info at the top of this page

On June 14, 2013 at 3:02am
vagos wrote:

at which states do you suggest charging an iphone battery ?
plugingi it in at 20% and remove it at 80% is that good ??

On June 14, 2013 at 6:05am
Randy Constan wrote:

@Paula: An electronic circuit is definitely the best way, because unlike NiCad cells which are not harmed by a constant trickle charge, a simple trickle charge on LiPO cells will eventually charge them to a voltage that degrades their longevity. There are good IC based LIPO cell chargers like the MAX 1555 if you don’t mind laying out a PC board to hold such a tiny part. It is also possible to make a simple self limiting charge circuit with a few ordinary size parts if you don’t mind a slow charge. For example, a 5V source such as available from a USB power cable can be routed through a couple of diodes and a 10 ohm resistor, as I described a few posts back. It will provide a 100mA charge that gradually tapers off to near zero as the battery gets to 4 volts. But even that circuit will eventually exceed the undesirable 4.2 volt point if left charging indefinitely. That’s fine if you don’t mind hanging a voltmeter across the battery and watching it charge, to disconnect at the ideal time. But for unattended charging its not such a good idea. After a lot of experimentation I’ve concluded that a dedicated chip or other precision circuit really is the best way to go.

On June 14, 2013 at 8:08am
Vince wrote:

If the current tapers off to zero as the battery reaches 4v, then how would it ever get to 4.2?

On June 14, 2013 at 2:16pm
Randy Constan wrote:

Well Vince, I observed it tapper off to zero, but looking closer and for a longer period of time it didn’t. It seems I didn’t take into account that forward voltage drop across an ordinary silicon diode can drop lower than I ever thought it could, as the current through it drops to NEAR zero. It took a long time for it to happen, but after several days, 5V through 2 Si diodes and a 10R resistor, the battery voltage actually made it up to 4.3. I doubt I’d ever leave the circuit charging for days like that, especially off a USB port cable which is hard to miss. So for a personal project this might be fine. But in my case I’m working on a project I’d like to consider marketing someday, so I decided to splurge on the MAX1555 and the couple of capacitors it needs to work right. And the max1555 does seem to work very well, by the way!

On June 14, 2013 at 3:29pm
Vince wrote:

Ah yes, I misunderstood.  I thought you were trickle charging it at 4V.  Now it makes sense.  Thanks.

On June 18, 2013 at 11:18am
Luken wrote:

Hi, I just got a new 1600 mah 3.7V Li-ion battery for my phone (instead of the original 1200mah 3.7V).

Charging from USB port, it says the battery is immediately full when its empty.

Using a 5.2V 1200 ma charger nothing happens at all, but this charger works on the old 1200mah 3.7V battery.

Any reason for this, other than that the new battery simply doesnt work?

On June 18, 2013 at 12:45pm
Randy Constan wrote:

Luken: I don’t want to make assumptions here… was the original; 1200mah also a Li-ion cell, or some other chemistry? If it was different, chargers are very specifically designed to watch voltage levels while charging, so a charger meant for one chemistry will be confused by another. The other question doesn’t make sense. Unless you left something out, I’m not sure how a 5.2v charger would apply to any Li-ion battery.

Also, I’ve seen several cases of LiPo batteries coming already fully charged. How do you know its’ “empty”? Does the phone work at all? Are all its metal contact points in exactly the same place?

On June 19, 2013 at 5:49am
Luken wrote:


The original was also Li-ion, yes.

Phone is completely dead with the new battery inserted. When “charging” the battery from the mains, phone remains dead. Charger light also periodically flashes from red (charging) to green (connected to mains, but not charging).

When charging from the USB port, phone charges for about a minute, then gives battery full reading. On disconnecting, the phone quickly loses life and dies.

Im confused by the voltage reading on the charger I received as well. Perhaps its meant to be 4.2V? Its a 3rd party charger. Seems to charge at a much faster rate, esepecially compared to the USB.

But in any event, bearing in mind that the charger works on the older low capacity battery, but does nothing whatsoever to the new what would your conclusion be from that?

On June 19, 2013 at 8:43pm
Vince wrote:

@Luken, two things:

First, this thing you call a charger, does the battery plug into it?  Or does it plug into your phone?  If the battery plugs into it, and it is putting out 5.2V, then it probably killed your battery.  But on the other hand, if it plugs into your phone, then it is not a charger.  It’s just a power source for your phone, and your phone itself is using its own built-in charger to charge your battery.

Second, while I don’t know if this is exactly your situation, the symptoms you describe sound consistent with a dead battery.  The phone, with it’s own internal charger, is probably very confused.  It thinks the battery is dead because it can’t supply enough power to make the phone function.  But it also thinks the battery is fully charged because it can’t accept any more power.  That is, if the phone’s charger is putting 4.2V to the battery, but the battery is drawing 0A of current, then it must be as full as it can get.  It’s conceivable that the connectors on the outside of the battery aren’t even connected to the cell itself.  (A battery actually contains a tiny circuit board for protection.)

On June 20, 2013 at 1:58am
Raton wrote:

if the battery is of 2000 mAh then what should be the charger current rating? if the rating is 2000 mAh then will it cause any problem ?

On June 20, 2013 at 8:16am
Vince wrote:

@Raton, battery capacity is measured in mAh, but current is just amps or milliamps, not milliamp-hours.  If a 2000 mAh battery is charged at a constant current of 2000 mA (2A), then it would theoretically go from empty to full in one hour.  In practice, it will take longer because as the capacity starts to get full, the current will taper off towards zero. 

But charging that fast is usually considered to be too fast.  I’d aim for something in the 200ma for a slow charge to 1000ma for a fast charge.  Slower is always better for the battery.

On June 20, 2013 at 1:43pm
Raton wrote:

will it destroy the battery ?? if charger is 1000 ma and battery is 1500mah then will there be any prob ??

On June 21, 2013 at 4:08am
Luken wrote:

You’re right its a power source for the phone I was referring to.

Looks like its a dud. Thanks for your help guys.

On June 21, 2013 at 5:14pm
Vince wrote:

@Raton, batteries are consumable devices, intended to be eventually destroyed by using them.  Charging them more slowly will destroy them more slowly.

On June 25, 2013 at 5:00am
Goutam Reddy wrote:

There are lithium ion cells that come with protection circuitry built in (e.g. Ultrafire 880mAH RCR123A ).  The protection circuit claims over-discharge, over-charge, and short-circuit.

What would be bad about using a dumb 4.2VDC (800mA) charger to charge a single, protected cell, instead of a smart charger with intelligent charge termination?

If I read the article correctly, the things to worry about are:
1) overcharging a pack (need to shunt current between cells to even out the pack charge), but this is a single cell.

2) over-voltage on a cell can cause plating, but I’m not going above 4.2VDC.

3) mini-cycles if left to charge at 4.2VDC and then internally discharging and then charging up again- but I believe this is a property of smart-chargers being left on, not dumb wall-warts just holding the voltage to 4.2VDC constantly?

4) over-current:  the DC adapter is limited to 800mA, so the max we can charge at is .9C anyway, which is within the 0.5-1C range.

Am I missing something else here? Thank You

On June 25, 2013 at 5:28am
Goutam Reddy wrote:

Yes, I am missing something:

The 4.2VDC wall wart will be delivering a lot of current to the battery, if for some reason the battery dips below 4.2V, because there is no resistor in the circuity limiting the amount of current.  So, while .9C is fine in the begging, it’s not good for extended periods… and will lead to plating?... and kill the life of the battery.

On June 25, 2013 at 1:34pm
Vince wrote:

@Goutam, good questions, and I would also like to know the same if anyone knows.  I’ve been operating under the assumption that a dumb charger is probably fine.  The battery itself will be limiting the current.  As it’s voltage approaches the voltage of the charger, the current will drop, and eventually become zero when they are equal.

On June 29, 2013 at 9:46pm
Joe Noel wrote:

what kind of charger is best for my Li-Ion 1100mAh 3.7v?

On July 9, 2013 at 4:04am
Jim wrote:

Is there an absolute minimum charging current?

I have a small solar panel that provides 12v at 0.2A.  I want to charge a 14.4Ahr li-ion battery pack.  The AC charger that comes with provides 12v at 1.2A so I would be providing 1/6 the current with the solar panel, would this hurt anything?

On July 16, 2013 at 9:54am
Vince wrote:

Hi Jim, No, there is no minimum.  The slower the current, the longer it will take to charge.  Your panel will just take six times longer to charge the pack, but no problem.

However, I am in a similar situation, and there is a different problem.  It seems that solar panels can be overloaded.  As the current being drawn by the charging device approaches the maximum the panel can provide, the voltage drops.  This is a particular problem on cloudy days, or in the morning/evening when your solar isn’t receiving perfect sunlight.  As the voltage drops, the whole system crashes for a second before recovering.  But the recovery may only last a fraction of a second, which can result in 80% downtime.

Here is an excellent article on this problem:  http://learn.adafruit.com/usb-dc-and-solar-lipoly-charger/design-notes

This is from a DIY kit for using solar to charge Li-Ion.  I have bought and built two of them, and can attest to the fact that they do work.


On August 4, 2013 at 2:36pm
Subutay wrote:

What is the max.working temparature for li-ion batteries.

My battery group contain 4 series 18650 cell group in 10 shunt battery and still temperature raising rapidly to 50 c and termal termostat is cut of the current in midle of the working progress.I am not sure the 50 c is correct working temperature.

On August 6, 2013 at 5:39am
Ping wrote:

0V Lithium polymer battery chargable. When Lithium polymer connected to product. It keeps in standby mode nearly 1 year. The Lithium polymer battery (Without protect circuit) from 3.7V drops below 0.08V. The battery can rechargable ( without protect circuit ) but it prevent by protect circuit. What is problem if charge 0V Lithium polymer battery?

On August 6, 2013 at 10:37am
Jez Xuereb wrote:

I have a LI Ion battery for mobilty scooter. It contains 2 cells and is rated 25.34V 218Wh.

Its charger needs replacing (it has an output of 29.4V 5A).
Can I use an electric bike charger - 25.90V 2A output ?
I do not mind if it takes longer to charge the battery.

On August 6, 2013 at 11:17am
Jez Xue wrote:

I need a backup charger for my mobility scooter battery.
My main charger has output of 29V 5A.
Can I use a bike charger with output of 24/29V 2A?

I think the battery has 2 cells and is rated 25.3V 218Wh.
Does the number of cells matter as to type of charger?

On August 7, 2013 at 8:17am
Vince wrote:

Batteries are usually rated at the nominal voltage, which is their normal, or average operating voltage.  For example, a typical lithium ion cell is 3.7v nominal.  It is full at 4.2v and pretty empty at 3.2v.  3.7v is its half way point.

So in your case, if you use a 25.9v charger to charge a 25.3v battery, you will only get it up to about half charge.  I don’t think it should hurt anything.  You just won’t be able to get a full charge out of it, which is probably around 29v.

On August 11, 2013 at 3:43am
Selvol wrote:

This site has been the greatest non biases source of info around for years.

Thank you

On August 11, 2013 at 5:34am
Jex Xue wrote:

Thank you.

On September 3, 2013 at 5:00pm
Damian wrote:

Is it possible to trickle charge a Li-ion battery using a portable solar charger?
and would this damage the battery?


On September 3, 2013 at 5:15pm
Damian wrote:

can Li-ion batteries be trickle charged via a portable solar charger?
and can this cause any damage to the battery?


On September 5, 2013 at 6:17am
Vince wrote:

As long as the charging voltage is correct (usually 4.2V) it wouldn’t matter whether the source of that voltage is from a phone’s charger, solar panel, or hamster in a wheel.  I have a series of contraptions for charging my batteries.  I have a solar panel that outputs 0-15.3 volts depending on solar conditions, which in turn powers a 12v-5v USB adapter, which sends 5v to anything designed to accept 5v, such as a phone or a standalone charger, which finally supplies 4.2v to the battery itself.

Things to consider when using a solar panel:  If you overload the panel, trying to draw more current than it can supply, possibly due to cloud cover for example, the solar panel output voltage may crash to zero.  This shouldn’t cause any harm, except that it won’t charge the battery, and may even drain it.

Also, while the solar panel must be in direct sunlight, take care to ensure that the charger itself, and the battery, are shaded and have cool.  Simply covering them with a dark panel may actually cause greater heat.

On September 14, 2013 at 12:21am
Enrique Batikoff wrote:

Excellent, very interesting paper covers a lot of subjects regarding design Lio charging methods to be employed

On September 14, 2013 at 12:29pm
Bill wrote:

If I put a 1.2V rechargeable battery in series in a 1.2V constant on circuit with a load:
1.  Will my total voltage be 2.4V ?
2.  Would this in effect be a trickle charger for the battery ?
3.  Might the battery discharge and, if so, should I use a diode between the battery and the incoming 1.2V ?
4.  Would it be best to use a Li-Ion, a NiCad, or a NiMH battery ?

This is a great site !!!


On September 19, 2013 at 12:14am
Nestoras wrote:

If i have my mobile phone plug on the charger overnight this will cause an overcharge?

On September 19, 2013 at 6:29am
Vince wrote:

Charge moves from higher voltage to lower voltage.  The only way to charge a battery beyond 4.2v is to charge it with more than 4.2v.

On September 19, 2013 at 6:32am
Nestoras wrote:

Dear Vince,
Thank you.

On September 29, 2013 at 9:18am
Milap wrote:

I have a problem with my li ion battery of my mobile.

It charges to 82% in about 2 hours 30 minutes and suddenly within 5 minutes it shows 100%.

Same with discharging…It discharges to 30% normally and within 5 minutes it shows 15%.

What can be the problem? i keep my phone switched off during charging..and charge only after battery reaches 0%.
I have also replaced the battery but the problem remains.Kindly guide me.

On September 29, 2013 at 11:20am
Vince wrote:

The good news is that you do not have a problem with your battery.  It’s just that your phone does not accurately know the percentage of your charge, so it guesses, usually based on usage.

Most phones usually charge the battery at 4.2v.  They can frequently (maybe once each second) watch how much current is going into the battery, and thereby “count up” how many mah of charge it is up to.  And the same process when discharging, counting down from full how much you’ve used.  You cannot accurately “measure” the charge left in you battery by looking at it’s voltage, because there is not a linear relationship.

As your battery ages, it is not able to store as much, so the phone may only charge what it thinks should be 82% of the battery’s capacity, but when the battery will suddenly not accept any more charge, then it realizes that it’s at 100%, as full as it’s going to get.

You could try a battery calibration procedure, which actually does nothing to the battery, but should help teach the phone what the upper and lower limits of the battery are.  However, what you’ve described yourself already doing is essentially the same thing. 

Ultimately, it sounds like a phone problem, not a battery problem.  I’d ignore it, personally, and just remember that 82% means almost full, and 30% means almost dead.

On September 30, 2013 at 1:59am
Milap wrote:

But my phone is new .

Just 1 month old and I am facing the problem since the first day.

Is there a defect in phone?

On September 30, 2013 at 10:15am
Vince wrote:

It may be a defect, or it may be a design problem, or it may be normal.

I’d ask the person you bought it from, or the manufacturer, if all phones of that model behave in that manner.  If yes, then that’s the way that phone was designed.  If no, then it is defective and they should fix it.

It almost sounds like it might be basing the reading on voltage, which is what I have my phone do by using an app called Battery Monitor.  By default, it shows 100% at 4.2V, 0% at 3.2V, and is linear in between.  On a fresh charge up to 4.2V it will show 100%, but drop almost instantly as soon as it is unplugged.  From there it drops very quickly at first, then spends most of it’s time around the 60%-40% range, where it changes very little, then once below 30% it will drop very quickly again.  I myself just learn to understand what these numbers really mean, and don’t take them at their face value.

On October 3, 2013 at 11:42pm

about knowledge

On October 7, 2013 at 3:37pm
Blake Cooper wrote:

In the paragraph that begins with, “Some portable devices sit in a charge cradle in the on position…” you say that the battery is being continuously discharged to 4.20 volts per cell; perhaps you meant 4.05 V instead of 4.20 V?
On another note, thank you very much for a great article; it is an important reference source for me.

On October 15, 2013 at 2:05am
Luciana Gama wrote:

Wow, this was the best article regarding Li-ion batteries I could find!
Congrats man!

So the old habit of charging the battery for the first time for a full day is long dead hahahaha
i remember this was recommended 10 years ago to extend battery life.
Well, I guess modern times are more practical. smile

Great, thank you for the information.
I just bought the new Galaxy note 3 and i will not let it charge for 9 hours… thanks!

On October 17, 2013 at 1:27pm
Luken wrote:

“Hi, I just got a new 1600 mah 3.7V Li-ion battery for my phone (instead of the original 1200mah 3.7V).

Charging from USB port, it says the battery is immediately full when its empty.

Using a 5.2V 1200 ma charger nothing happens at all, but this charger works on the old 1200mah 3.7V battery.

Any reason for this, other than that the new battery simply doesnt work?”


Hi I left this email a few months ago. Your response suggested it was the battery at fault. But I’ve got the provider to send out a new battery, and that didn’t work either. They have a good rating, and are unlikely to sent me 1 nonworking battery, let alone 2, which were both brand new and untouched.

So 3 batteries-2 newer 1600mah batteries that dont work at all, and one old 1200mah battery that doesn’t last a day, which I’ve been using since.

Any suggestions/possible faults other than the battery?

On October 17, 2013 at 5:14pm
Vince wrote:

Assuming that the battery is good, then it is either empty, full, or somewhere in the middle.  To find out, leave the battery off the charger for a couple hours, then use a multimeter to measure the voltage between the + and - terminals.  Anything over 4v is pretty full, and anything under 3.4v is pretty low.  3.7v is nominal, average, half way.

If the battery is bad, it could read full, and yet not be able to supply enough current to power your phone for very long.  But we’re assuming that the battery is good.

If a good battery is full, but won’t run the phone, then the phone is bad.  If a good battery is empty but won’t charge, then the charger is bad.  Remember, the charger is either built into the phone, or you may be using an external charger, which is a cradle the battery sits in.  The power cord for the phone is not a charger, only a power cord.

On October 18, 2013 at 10:59am
Teacher Tom wrote:

Great info…
I cannot find any info on how to use Li-ion with solar cells in a solar car.  Our High School is building an electric three wheeler with solar cells to augment the power of our 11.2V, 60Ahr x 7 packs. Can we charge and run at the same time or do we need to manage our use switching between both power sources charging only when we are stopped?

On October 19, 2013 at 8:56am
Vince wrote:

I don’t know anything about solar cars, but I’d say that any additional power source you provide to the car will be that much less that the battery has to provide.  I assume your solar source can’t provide enough to keep up with the demands of the car while it’s in use, or you wouldn’t need a battery.  Wouldn’t that be nice!

So without using any real numbers, let’s say a load needs 20 watts, and a charger can only provide 10 watts, then for every hour you use the device, it would take twice as long to recharge it.  But if you’re applying the source and the battery together, then the device can get 10 of it’s required watts from the solar, and now the battery only has to provide 10 more, and so you can use the device for twice as long before the battery is empty, at which time the device would try to get all its power from the solar source, which can’t provide enough, and you’re dead in the water until you recharge.

On October 19, 2013 at 9:01am
Vince wrote:

I should also mention, and probably you already know, that I didn’t take into account the different voltages involved, and so you would need some circuitry to make things like they need to be.  For example, a typical laptop computer power cord supplies 19v.  But the battery may only be an 11v battery.  So obviously the power management thingy in the computer has to make sure the proper voltage goes to the proper destination.

On October 27, 2013 at 4:54pm
Ian wrote:

By laptop battery (lithium ion) does not charge beyond 93% which is ok with me but when it discharges to 26% power goes as if it had reached 0. Why is this, can anything be done to correct it?

On October 27, 2013 at 5:28pm
Vince wrote:

As you use batteries, they lose some of their capacity.  Your laptop isn’t aware of the battery’s diminished capacity. 

Some laptops allow you a calibrate the laptop for the battery, basically by going through a full charge and discharge cycle, while the laptop monitors the charging and discharging process to learn what the battery’s capacity is.  This calibration function is usually found in the BIOS, if it exists.  Many laptops don’t have any means for recalibration.

Alternately, you can just learn and remember for yourself that 93% means full and 26% means empty.  Also you may be able to reconfigure the power options through the Control Panel.  For example, you might tell it to display an alarm at 30%, and then go to sleep mode.

Lastly, you can buy a new battery on ebay, usually for under $20.

On October 27, 2013 at 6:20pm
angelica wrote:

What’s the difference between a protected and unprotected battery? If I’m making various serie/parallel conection what’s best?
Also If i decide to use a PCB battery, it’s best is a buy unprotected batteries and use PCB board or it’s best to buy cells with the PCB include??

On October 28, 2013 at 8:51am
Vince wrote:

From the website batteryjunction.com, “Li-Ion and Li-Poly battery packs should always be used with a protection circuit to prevent the cell from over charging or over dis-charging. Choosing the correct circuit and applying it appropriately is vital to the longevity your batteries and your own safety.”

All of the batteries I’ve bought have come with PCBs (Protection Circuit Boards).  Even if you’re making your own battery of batteries, I’d recommend using individual PCBs on the individual batteries.  Whether you want to buy with the PCB or add your own probably depends on your level of expertise. 

On November 4, 2013 at 7:34am
Kevin wrote:

Hey Vince

Thanks for the useful info. I just have one question: I know you said its better to turn off the device when charging to prevent parasitic load. But let’s say I’m at home and want to watch netflix on my phone, or work on it for a few hours, and I’m close to a charger. Is it better to keep my phone connected to prevent battery drain, or is it better to just use the battery and charge later?

On November 4, 2013 at 7:35am
Kevin wrote:

Hey Vince

Thanks for the useful info. I just have one question: I know you said its better to turn off the device when charging to prevent parasitic load. But let’s say I’m at home and want to watch netflix on my phone, or work on it for a few hours, and I’m close to a charger. Is it better to keep my phone connected to prevent battery drain, or is it better to just use the battery and charge later?

On November 4, 2013 at 8:31am
Vince wrote:

A reminder to all:  I am not in any way related with this website, the original article, or the author thereof.  I’m just a normal reader like the rest of you.  Any advice or information in the original article didn’t come from me.

@Kevin, I’ve thought about this myself.  I go through a lot of batteries, because I use them and abuse them.  I normally prefer the convenience of not being plugged in.  However, in response to your question about what’s better for the battery, I think maybe it’s best to have it plugged in while you’re using it the heaviest.

What’s absolutely best for the battery?  According to what I’ve read, charge it up to about half way, maybe 3.7-3.8 volts, remove the battery, sit it on a shelf, and don’t use it.  Maybe once a year, check it and charge it back up a little if needed.  This will probably make it last the most number of years, because you’re not using it.

That’s not practical in the real world.  We buy them to use them.  So what’s the next best thing?  Don’t use them any more than you have to.  So if the power being drawn out of the battery is the same as what would be going in to it when charging, then they cancel each other out, and essentially you’re not using the battery, and your phone is basically running directly off of wall power.

I think probably the best thing in this scenario is to put it on the slowest charger you can find, such as a computer’s USB port which is limited to 500 mA (0.5A). 

A perfect example is when I’m on the road, running the GPS with the screen on continuously, while streaming internet radio in the background.  I’ve noticed that I can drive all day long and never get a full charge, even though it’s plugged in.  So in this case, I’m using zero charging cycles. 

If this seems contradictory to the advice about parasitic load, let me add this:  Any load, parasitic or otherwise, will increase the time needed to achieve full charge.  But once it is fully charged, a smart charger will stop charging all together until the voltage drops down to a predetermined “switch back on” level, maybe 4.0v for example.  If the phone is on and you’re not using it, this will result in unnecessary charge/discharge cycles.  So if you don’t need to use it while it’s charging, overnight for example, then yes, it’s best to turn it off.

On November 15, 2013 at 6:37pm
Matthew Cushman wrote:

What I’d like to hear more about is the behavior of a lithium ion cell under fast/high temperature discharge conditions.  Does discharging too quickly or allowing it to get too hot while discharging (or let’s say, both at the same time) cause permanent damage or not?  I have a tablet with an >8000mAh rated battery that manage to discharge itself from about 90% to about 20% in the course of a couple of hours, and when I got to it its temperature had reached 130F/54C and was hot enough that I could smell the plastics in the device starting to outgas.  I’m glad I noticed it when I did - who knows what could have happened?  Should I be concerned for the battery’s condition now?

On December 31, 2013 at 5:42pm
princess wrote:

hi everybody. I have a smartwatch here which I’d probably overcharged it accidentally for more than 12 hours. The battery it runs is the 80 mAh Li-Ion. After i removed that.watch from the cherger. It isn’t responding anymore.. So how can I actually restore.my battery? Do i need to wait for a while? This is really stressful because thsi watch is so expensive, help pleasee..

On December 31, 2013 at 5:53pm
Vince wrote:

It seems unlikely you would have overcharged it.  You could check the voltage of the cell with a voltmeter.

On January 1, 2014 at 8:06pm
Irnest wrote:

Hi All

I’ve read quite a bit on Battery University and I think this is an excellent resource. Thank you to the creators.

My question revolves around the usage of mobile phones and tablets, particularly ones with batteries that are NOT removable. In my case, the iPhone and the iPad from Apple.

If I understand what I have read correctly, the following practices are better:
1) its better to charge it NOT when its run down completely (say 0% on the phone’s battery percentage indicator) but to rather charge it when it gets to say 20%.
2) its better to unplug from the charger NOT when it gets to 100%, but say 80%. This practice is supposed to lengthen the total life of the battery significantly
3) the final thing I’ve picked up is that its better to switch the device off while charging.

My comments on the above are that these are not very practical.

Firstly, depleting from 80% down to 20% only gives you a usage of 60% of the battery’s capacity. So this advice is supposed to lead to longer overall battery lifespan, but it’s effectively cutting the battery’s capacity in half for practical day to day use. This would be possible for a phone with a removable battery, but not for the iPhone.

Second, turning the device off while charging (say overnight) is also not practical for those that want the phone on in case of emergency calls.

So, while I appreciate all the advice and have enjoyed improving my knowledge, I struggle to understand how to practically apply it.

Have I missed something?

On January 1, 2014 at 8:52pm
Vince wrote:

Hello Irnest.  No, you have not missed anything, unless it is the purpose of the practices you mentioned.  The first two are to maximize the longevity of the cell, and the third is for faster charging.  You are correct that following practices to make the cell last as long as possible is not practical for someone who wants to get the most use out of their phone or tablet. 

It’s kind of like telling a race car driver how they could increase their fuel economy.

It’s unfortunate that some manufacturers, especially, but not exclusively, Apple, have made the cells non-user-replaceable.  They expect you to buy a new device when the battery dies.

The best suggestion I can give you is about your practice #3.  While turning the phone off will make everything last as long as possible, whether you’re charging or not, it’s actually more important to have it plugged in while you’re using it the hardest, so that you’re really not using the battery any more than you have to. 


On January 10, 2014 at 2:20pm
YS wrote:

This is the greatest post about Li-ION batteries I’ve ever read!

Before reading this article a Li-ION battery charge method seemed like a mystery to me, but now I think I clearly understand it. Thanks a lot!

BTW, it turned out to be a lot simplier than I imagined.

On January 12, 2014 at 8:46am
Vivapo wrote:

I bought a new Moto G phone and it came without a charger. Manual says that all microUSB chargers that give current between 500-1500mA is fine. I have two choices for the charger, 750mA or 1200mA and I’ve been thinking about that which one is better in the long run?

(I know that at with smaller charger charging time will increase but it would be a problem for me if it would improve the battery lifetime significantly.)

Which charger should I choose?

Best regards, Vivapo

On January 12, 2014 at 9:01am
Vivapo wrote:

..I forgot to mention that this phone has a 2070mAh battery.

On January 13, 2014 at 2:00am
Vince wrote:

@Vivapo:  Yes, the phone did come with a charger.  It’s built into the phone.  What you’re looking at is only a power supply for the phone.

The charger in the phone will charge the Li-Ion cell at 4.2v.  The power supplies you’re considering will all put out 5v.  If we ignore this difference for the purpose of simplicity, we can estimate the amount of time for full charge simply as either:

2070 mAh / 750 mA = 2.76 hours, or

2070 mAh / 1200 mA = 1.725 hours.

Slower is always better for the longevity of the cell, though less convenient.  If you don’t mind waiting for almost three hours to charge from completely dead to full, then go with the 750.

But really, you have more than those two choices, as microUSB is a standard.  Just go to ebay and search for “micro usb wall”.  You can ignore brand and model, because USB is USB, so a cord for a Samsung, LG, Nokia, etc., will work just fine with Motorola, and vice versa.  They’re so cheap, you can buy ten of them for $10, and put one in every room of your house.

On January 13, 2014 at 2:12am
Vince wrote:

For example, check this out:  http://www.ebay.com/itm/Wall-Car-Charger-Flat-Micro-USB-Data-Sync-Cable-for-Samsung-Galaxy-S4-S3-Note-3-/291005937740?pt=LH_DefaultDomain_2&var;=&hash=item43c14e384c

On January 15, 2014 at 9:21am
Jovie Brett wrote:

Great article! At last I fully understand what different charging ways are :D Thank you!

On January 16, 2014 at 10:15am
Sonny Eriksson wrote:

I am starting to doubt the battery university in this article.

It says that with a 3.9 V charge you receive 76 % capacity. While you on the other hand says in the article Howe To Prolong Batterylife that you only receive 50 % CAPACATY at 3,92 V.

Hope you are able to correct me in this matter.

Regards Sonny

On January 16, 2014 at 11:15am
Vince wrote:

I don’t think anyone associated with this article reads this anymore, or at least hasn’t chimed in in many years.

I agree that those numbers don’t sound right.  Since a typical lithium ion cell has a nominal voltage of 3.7v, I would expect it to be at 50% capacity at that nominal 3.7v range.  Understandably, due to the non-linear voltage/charge relationship, it may be very close to 3.7v from way above 50% to way below 50%, as I have observed with my phone.

On January 22, 2014 at 12:34am
Mark_BC wrote:

Why is it that when I measure using my multimeter the voltage on the contacts of my Gopro battery charger, I get 4 V DC which makes sense, but then when I flip it to AC measurement, I get 8 V AC?

On January 22, 2014 at 9:46am
Vince wrote:

If you try to measure Alternating Current voltages when there is no Alternating Current, the readings you get will not be meaningful.

On January 22, 2014 at 2:28pm
Mark_BC wrote:

I thought trying to measure AC from a DC signal will give you zero on the meter.

So basically is it true that Li ion batteries get charged with a simple constant DC voltage, not AC?

On January 22, 2014 at 5:11pm
Vince wrote:

Yes, simple DC.

Out of curiosity, I just measured some batteries on AC with a couple different meters.  The results varied by brand of meter.  The cheap Harbor Freight meter did show 8v AC.  My Actron meter showed 0v AC.

It makes more sense to get zero measuring DC on an AC source, because the average is 0 (between +120v and -120v, for example).  But I don’t know how it would measure AC on a DC source.

On January 27, 2014 at 9:31pm
Peter Krauliz wrote:

This article doesn’t explain required necessary basic CONNECTING and DIS-CONNECTING procedures between a CHARGER and a BATTERY. There are inconsistent instructions in respective device-manuals around when they refer to MOBILE PHONES, BEARD TRIMMERS or LAWN TRIMMERS; just to mention a few devices. I understand that the sequence of ‘what to connect or disconnect first’ relates to battery life and/or battery safety, and should be clearly described. Shouldn’t there be a clear preference? Can the author or posters help with that? Thanks very much in advance.

On February 20, 2014 at 8:52am
nativ wrote:

Hi there, I just realized this site doesnt tell you if its DETRIMENTAL IF YOU CHANGE THE RATE OF CHARGE (to FULL CHARGE). for example… charging to full charge for 2 HOURS and then using a different charger whch charges to full charge after only 80 mins.

Would this affect the LONG TERM battery capacity or life span???

On February 20, 2014 at 1:38pm
Peter Krauliz wrote:

Has the author lost interest in responding to questions?

On February 20, 2014 at 1:46pm
Peter Krauliz wrote:

I have clicked on a link that removed me from receiving further notifications without warning me that the removal would happen at the same moment. That was pretty stupid from either side. I am asking for undoing the REMOVAL and getting a response to my original question which had been:

“This article doesn’t explain required necessary basic CONNECTING and DIS-CONNECTING procedures between a CHARGER and a BATTERY. There are inconsistent instructions in respective device-manuals around when they refer to MOBILE PHONES, BEARD TRIMMERS or LAWN TRIMMERS; just to mention a few devices. I understand that the sequence of ‘what to connect or disconnect first’ relates to battery life and/or battery safety, and should be clearly described. Shouldn’t there be a clear preference? Can the author or posters help with that? Thanks very much in advance”

On February 20, 2014 at 3:02pm
Vince wrote:

Hi Peter, I don’t have any idea who the authors are, but I don’t think they’ve responded to anything here in years.  It’s doubtful that anyone affiliated with this site even reads these comments.  However, at the top of this page, there is a “contact” button.

On February 20, 2014 at 6:54pm
Peter Krauliz wrote:

Thanks Vince. Your advice is helpful.

On February 26, 2014 at 7:01am
The Lightning Stalker wrote:

Why has information been removed from this article? There used to be detailed charging information, but it has been removed, why?

On February 26, 2014 at 8:34am
Vince wrote:

Any idea what has been removed?  I’ve been lurking around here for a couple years now, and don’t recall reading anything before that’s not there now, though that’s not to say I would remember it anyway.  I think I’ve learned just about everything I’m going to from this site, but if there was more, I’d be curious to know what it was.

On March 1, 2014 at 9:27am
petepablo wrote:


I have a couple questions I hope u can answer, I recently bought an extended battery for my samsung s3 3000mah.

Longevity is more important to me than run time (extended battery I don’t need to charge to 100% anymore as it should easily last a day using only 50%)

My questions are what are the best way to charge it upon new?

It’s a lithium ion battery and I’ve been reading conflicting comments and posts with people saying to cycle it for the first 3 times, full charge discharge etc to maximise the capacity of the battery or for it to reach it’s potential.

Do you think that is just superficial as in it’s a calibration thing or do you believe it actually might increase/reach the full potential capacity by doing such initial cycles?

I thought letting battery charge to 100% and fully discharge would damage the batteries longevity even if only done 3 times? What’s your take on that?

Also, if I don’t do the initial charge discharge full cycles would that stop me getting the maximum potential of the battery long term?

I’m in 2 minds what to do and thinking to do it just to be on the safe side.

So far I used it to 18% then fully charged overnight for over 8 hours (the first charge) thensecond I charged from 38% to 100% (but took it off charge when it said 100% but the light hadn’t turned green) do you think that would impact my battery in any wayfor better or worse?

Everywhere I read says it takes a few charge discharges before the battery reaches it’s full capacity - what’s the science behind that? I can’t find a proper explanation
I did notice that with my first original 2100mah battery where it got better after 3 charges.

Would me not following the procedure have a negative impact on the battery after the 3 initial charges is up? Ie if I don’t do it now it’s too late.

I’ve noticed my extended battery drops from 100% to 80% very quickly so seems like it’s not lasting as long I’d hope it or should be doing. Can’t explain. Seems better between 80% to 40% but still unsure, feel like it should be lasting longer than it is.

On March 1, 2014 at 10:14am
Vince wrote:

Hi petepablo,

From everything I’ve read, the idea about fully charging and discharging to get the most out of it is from the old NiCad cells, and is not applicable to Lithium Ion.  But old habits die hard and people who don’t know the difference may still recommend wheat they heard in the past, even though it is no longer relevant. 

I’ve read that LiIon only have so many cycles of life, and so intentionally discharging it like that only shortens its lifespan.

In my opinion, the best way to make the battery last the longest is to not use it, or to use it as little as possible.  For example, if I’m driving down the road using it for GPS with the screen on, that requires a lot of power, so I have it plugged in during that time.  If I use a weak enough power source, it might never charge at that rate.  That is, the phone is using energy as fast as the power cord is supplying it, and the amount going to or from the battery is minimal, so I’m not subjecting the battery to any charging cycles.

Another thing to do is to not hold the battery at full charge, because apparently that puts a lot of stress on the battery.  If you could find an app that limited charging to 75%, then you could leave it plugged in all the time.  I don’t know of such an app, but I haven’t looked.

Now in answer to another of your questions, it’s very inaccurate to assume remaining charge based on voltage, because the voltage drop during a constant discharge from full the empty is not linear.  The voltage drops a lot at first, then almost levels out for most of the cycle, and then drops quickly near the end.  So if your device is using the voltage to estimate charge, that might explain why yours quickly goes from 100% to 80% as soon as you unplug it.

Because of this, many devices sample the current being used, and use this to count how much energy is used and remaining.  Imagine if you know your car can get 400 miles to a tank of gas on average, and you only keep track of how far you drive to estimate how much gas you have left, instead of using your fuel gauge.  That’s kind of how my phone works.  But because that may change over the life of the battery, some people want to recalibrate their phone from time to time.  This is where the complete discharge/charge/discharge procedure comes in.  It doesn’t do anything to the battery but wear it out faster, but it helps the phone learn how much use the battery can provide on a full charge, so that it may better estimate the remaining capacity during normal use.

It’s hard to tell how the battery’s doing without timing it all the way until the phone dies on its own.  Especially using an extended battery.  Since my phone doesn’t understand how I can possibly have this much capacity (I use 3800mAh batteries instead of the 1500mAh the phone was designed for), the reading will go down to 1% and still last for another day or more.

Now here’s another thing to consider with extended batteries:  The hone might pump a full normal battery’s worth of charge into it, and read “full”, even though the extended battery can actually hold much more.  So that’s why many extended battery instructions say to keep it on the charger for a longer time, even after the phone says it’s full.

I hope this info is helpful.  Enjoy!

On March 1, 2014 at 4:11pm
peteypablo wrote:

@vince thanks for the response

I see you’re of the train of thought that the initial charge discharge cycle makes no difference but im referring to people who have actually tested out this discharge full chargr cycle for the first 3 charges and actually have results to prove it..do you think it literally is just a calibration thing OR the fact apparently after a few charges it suddenly grts better (I noticed this on my 2100mah samsung s3 battrry as mentionex the original one, I didnt charge discharge but after the 3rd charge it inexplicably got bettrr.

Do you think the reason for the results people have had for lithium ion chsrgr discharge cyclrs initially is just coincidence and it would have happened anyway after 3 charges partially?

What I cant figure out is WHY after 3 charges do lithium ion batteries perform better like what is the science behind it?

I cannot find the reason on the internet or even a possible theory.

I agree with your plugging in the csr charger while using gps in the car but I find that woukd damage the battery even quicker esp in a samsung s3 as it gets really hot while in use and charging so wouldnt make sense as any extra gains u get from not using the battrry while plugged in is more than cancelled out by the extra heat damaging thr battery. Maybe yours is different.

Basically as you are saying that even if I don’t do the initial full charge discharge

On March 1, 2014 at 4:15pm
peteypablo wrote:

It wont affect the potential of the battery as in id be missing out?

I have a samsung oem extended battety 3000mah so I assume it’s made as the original 2100 onr it came with.

longevity is more important to me so I think I’ll just charge it from 30-80% now ive done thr first 2 charges to 100%.unless there’s a good reason to do a full charge discharge

On March 1, 2014 at 4:56pm
Vince wrote:

Hi peteypablo,

I’m no expert, so I couldn’t tell you the science behind any of it.  But from everything I’ve read, I can’t imagine why going through three discharge/recharge cycles would make any difference.

But more importantly, I don’t know how you could even tell if it made a difference unless you timed exactly how long it took to completely die from a full charge each time.  I suspect many people might assume the battery is lasting longer because the phone is reporting the capacity dropping more slowly, but the phone is only guessing based on usage.  I suspect the three discharge/recharge cycles may be allowing the phone to learn better what the battery’s true capacity is, and thereby reporting it more accurately.

I think the only way to know for sure is to make some device that draws a consistent amount of current from the battery, say 100ma, and you time exactly how long it takes the battery to go from 4.2v to 3.2v, then completely charge it back up again, and repeat the test three times.  This would be a great experiment for some kid’s science project, don’t you think?

On March 2, 2014 at 4:21am
peteypablo wrote:


I was thinking about what you said about the phone noy recognising the 3000mah eztended battery and only charging a normal 2200mah full..

is it possible samsung would do that?

I notice it’s only on. 70% charge and it’s already at 4120mv which seems a bit high?

Would I need to get a battery monitor that charges it ptoperly

On March 2, 2014 at 7:57am
Vince wrote:


I like to imagine charge as a thick goo, and a battery as a big shallow pan, which you only fill from one corner, and the voltage is the height of the goo at that corner of the pan.  Because the goo is very thick and sticky, when you’re filling the pan, the corner that you’re filling will get full first, but if you wait long enough, all the goo will eventually even out throughout the pan.  And when you drain the pan, that corner will drain first, while most of the rest of the pan still has a lot of goo in it.

And if you look at the table at the top of this article, you’ll see that the voltage of the battery will reach 4.2v long before the battery is fully charged.

The best way to tell how full a battery is from the voltage, is to wait an hour or more after it’s unplugged from the charger.  This will give the charge time to saturate throughout the battery, and then when you measure the voltage, you’ll find it’s not as high as you first thought it was.

I’ve noticed the same thing happens during discharge.  If I’m using the phone for a long time, video, gps, or anything that keeps the screen on, the voltage will eventually read very low.  But after I quit using it and wait for a while, the voltage will come back up on its own, even without being plugged in.

So voltage can really only be used as a charge indicator after the battery has been sitting idle for a long time.  While charging, a better indicator is how much current is flowing into the battery.

When you first plug in your phone, the battery will suck up the juice as fast as your charger will provide it, until the voltage of the battery reaches the voltage of the charger, 4.2v.  After that, the battery will continue to suck up more charge, but the rate at which it sucks it up will decline as the battery fills up, and will eventually slow to a trickle. 

There will always be some current due to the inefficiencies of charging, especially if the phone is on while being charged, but even if it is off.  So the current will never reach zero, but when the current is close to zero and has stopped decreasing, then the battery is as full as it’s going to get.

On March 2, 2014 at 4:58pm
peteypablo wrote:


I think im going to follow your recommendation of looking at the voltage as a guude as oppose to the %. At the moment I charge it around 35% to 80% ie avoiding the saturation charge..however from your previous explanation I realised that % is not a good guide..at what % should I be charging from/to?

I’ve noticed that it hangs around 3908mv below 80% which makes me thibk that maybe 77% is probably just as it hits the saturation charge level?

What mv should I be looking at as a guide? I still don’t fully understand it but that’s not important

On March 2, 2014 at 5:12pm
peteypablo wrote:

@vince yeah I agree it be a great science experiment and would help to answer some unaswered questions from doubters and limit the debates whether charging discharging initially improves the battery capacity.

also vince as I mentioned before your idea about charging while using gps navigation in the car seems like a goos idea however the extra heat from both charging amd the screen on the whole time would kill the battery surely? Mine reaches 40C! Just having the screen on for an extended period of time at a higher brightness (tho air con I guess would bring it down but im from a cold environment) without even charging. .how do you avoid the damage done by the extra heat?

I think I’ll either by a satnav instead or juat rely on the extended battery

I honestly don’t know how much votage charge my battery is getting but I like to avoid the 2 extremes of 4.2V charging and also below 20% where it puts strain on it.

On March 2, 2014 at 5:37pm
Vince wrote:

I think the best thing you can do, for what you want, is to make sure you always charge it slowly.  This probably means not using a wall or car charger, but only charging from a computer’s USB port.  USB port standard maximum output is only 500mA, so that will help a lot.

Regarding how I use it for GPS without damage, if the current being supplied equals the current being consumed by the device, then the battery really is neither being charged nor discharged.  It’s just kind of sitting there idly.  The phone will get warm from the screen and all it’s thinking, but the heat is not coming from the battery.

Here are a couple apps you might find interesting.  I don’t use either of them, so I can’t tell you anything about them, but they look like they’re written for you!



On March 3, 2014 at 3:42pm
Peter Krauliz wrote:

I’ll never get an answer to my questions I sent some weeks ago. I am off and out for good. Thanks for good will anyway, to whoever thinks it may concern them .

On March 8, 2014 at 10:42am
peteypablo wrote:


I find that if I charge via computer usb it overheats when I charge my blackberry with usb charger it charges really slow and overheats the cable and phone feels more.

the issue is that 4.3 android does not let you reduce brightness lower as it was on 4.1.2, im in the lowest brightness setting yet it’s still brighter on 4.3 than lowest setting on 4.1.2.

I think that’s the biggest contributer to battery drain, the extra heat etc.

im not sure what to do apart from going back down to 4.1.2 which is hassle.

even with my extended battery it only lasts slightly more than using a normal 210mah battrry on 4.1.2. Very annoying tbh. Plus on 4.3 it charges slower and heats up quicker

On March 8, 2014 at 11:55am
Vince wrote:

hmm, strange.  I guess I don’t know what to tell you about that.  Yes, charging from USB should be slower, and that’s the point, but it should charge cooler, not warmer, so it sounds like something’s wrong. 

On March 8, 2014 at 9:53pm
zac wrote:

Thankyou for the primer on lithium ion batteries.  I guess I’ll just be charging my devices only partway so i can preserve service life.  I’m happy to sacrifice run time in exchange for longer service life.
Also, nice tip about turning off the device when charging.  I suppose this is why so many GPS batteries have died… i was charging the battery while using it.
I used to design battery chargers, and I like this article.  It gives me enough to design the charger for this chemistry.  There’s also chips from several manufacturers that will do the same.

On March 11, 2014 at 2:11pm
peteypablo wrote:


something you mentioned earlier about that with extended batteries the phone or apps may not recognise the extra capacity and therefore only charge it to the standard original battery capacity..

I used battery doctor app to speed charge the extended battery but rrading the stats it says maximum power 2100mah which is incorrect as it’s a 3000mah battery..I did notive it charged quicker but maybe because it’s thibking it’s a 2100mah battery.

I I want it to charge properly to 80% would I be better off just letting the samsung s3 stanfard charge it instead?

I cant be sure whether I’m even getting maximum capacity out of the battery or whether it’s only charging as if it’s a 2100mah battery.

What do you think would be best?

On March 12, 2014 at 1:15am
Vince wrote:

Out of curiosity, I just installed the battery doctor app.  I’m wondering what it says about mine.  Where did you find the stat that tells you maximum power 2100mah?

On March 15, 2014 at 10:55am
peteypablo wrote:

@vince sorry for the late reply

I unibstalled the app but from what I remember is if you click below the circle the little icon is clickable and bringa up battery info. Id be curious to know what yours says.

I reread this document and im confused still what is the optimum voltage to take the charger off?

Im trying to follow what you said about voltage rather than percentage.

According to this document what is the voltage when it starts to add saturation charge? And what voltage should I be topping up the charge?

At the moment I am doing it at 30% and taking it off at 80% but I need to look at the mv, what is the ideal mv I should start charging at and max mv I should take off for prolonging battery life long term?

On March 15, 2014 at 3:51pm
Vince wrote:

I uninstalled the app also.  I didn’t see any advantage to it, and I know it was wrong, because it would report the same percentage that my phone would report, while I could tell from my voltage that I had a lot more juice left.  And indeed, both my phone and the app would say, for example, that I was at 1% (it never says 0%), and it would last another day.  So I uninstalled it.

I don’t think there really is any “optimum” voltage at which to stop charging, as it’s just a trade-off.  If you could start charging it as soon as it fell to 3.6v, and then stop charging it as soon as it reached 3.8v, that would be great, but how inconvenient!

The manufacturers have decided that 4.2v is the “optimum” tradeoff between longevity, runtime, and convenience.  So that’s what the chargers inside the phone, and most other stand-alone chargers, are designed for.

Besides, how can you measure it?  If you pulled it off the charger at 4.0v, as soon as you pulled it off, it would fall way below that.

It probably starts the “saturation” phase as soon as it reaches 4.2v, but what real capacity it’s at at that point is unknown.  If you were very slowly charging it, it might be mostly full.  But if you were charging it quickly, then it might not even be half way yet.

I think the only way to know for sure, would be to first make sure it really is completely fully topped off, then don’t use it, and time exactly how long it takes to go dead, which would be several days.  This would tell you it’s maximum runtime, which would be indicative of the maximum capacity.  Then you could quick charge it, and unplug it as soon as it hits 4.19, and see again how long it lasts.  The ratio of the two would be how full it was when you unplugged it after fast charging.  You could also repeat the test after slow charging, and see the difference.

To really top it off, I’d leave it on the charger all night long.

On March 16, 2014 at 6:53pm
peteypablo wrote:


You mentioned that you would reach 1% and knew it was incorrect, at what voltage was it at the time?

Im finding that the stock samsung battery measure in the device ia relatively accurate in that when I use thw oem 2100mah battery and the oem 3000mah extended battery there ia a significant difference in run time between them as in it lasta longer by abou a 1/3rd and takes longer to charge to 80%

I just don’t follow rhe article too well and want to know roughly what ia best like I said I charge from 30% to 80% as I assumed that was where satueation charge kicked in but you said I should look at the voltage but what amount wouls you say roughly?

Also how low before it’s too low, it could well be I should be chsrging at 40% but I dont know what ia the ideal voltage ro charge to prolong battery life.

Ia it the 3.6v and 3.8v like you said?

On March 16, 2014 at 7:32pm
Vince wrote:

On mine, my my voltage would be about 3.7 to 3.6v when my phone would say it was dead.  That kind of makes sense, as it was designed for a 1500mAh battery, and I’m using 3800mAh batteries now.

The process of totally topping off the battery, then letting it drain all the way down to dead, and recharge it all the way back up again, is supposed to let the phone learn the battery’s capacity, to calibrate the phone to the battery.  But it’s never worked for me on my phone.  So I gave up trying it, or thinking about it too much, and now I just simply use the dang thing.

As far as what’s optimal for the longevity, I mentioned 60/40, but really, if you could hold it at exactly 3.7v, which should be 50%, and charge it any time it drops below 3.7v, and stop charging it as soon as it gets over 3.7v, that would probably be optimal for longevity.  Everything else is a tradeoff between optimal longevity and personal convenience.

As for the “saturation charge” kicking in, I don’t really think there’s a certain type of charging that kicks in.  I think it’s just that, let’s say your battery is down to 3.3v, and you connect it to a 4.2v charger that can put out 2A, (2000mA).  As long as the voltage of the battery is less than the voltage of the charger, the only limiting factor on the current is how fast the charger can put it out.  But once the battery reaches the same voltage as the charger, the current starts dropping, not because the charger is doing anything different, but because that’s just all the current the battery can draw.

And again, I don’t think there’s a certain percentage where the battery reaches that point, but that it probably depends on how fast you are charging it.  So if you’re charging it at only 500mA (standard computer USB), then by the time the battery first reaches the 4.2v “saturation” stage, it may already be 95% full, but if you charge it more quickly, like at 2000mA, then it might be only 50% full when it reaches the same point.

And those aren’t real numbers.  I’d imagine that the size of the battery also factors in to it, so what’s considered a fast charging rate for a small battery might be a slow rate for a larger capacity battery.

And I don’t really think there’s any way for normal people like us to ever know whether any of this is making a difference or not.  If one person’s battery pukes out after two years and another person’s doesn’t, how can we tell if it was because of charging habits vs usage habits, manufacturing differences, climate, etc. 

On March 17, 2014 at 6:51am
peteypablo wrote:

@vince thanks for the advice.

So I assume charging it when it drops below 3.7v is ideal for longevity.

I think for coming convenience I’ll charge to 80% and when it drops to less than 3.7v I’ll charge it.

I think the problem is if take it off at 3.7v that’s only like 60% which isn’t enough to get metthrough the day.  So its a trade off of whether I charge to 85% and charge at 35% or charge to 75% and charge at 25% I don’t really know which is better/worse for the battery stress wise? I guess I have to look at the voltage

Ideally on the bottom end how long can I let the voltage go before recharging without it causing long term damage? I notice the voltage is around 3.4v at 30% so maybe I should charge at 40% if I’m at home and not in need of more juice.

I use os monitor app for checking battery temperature and voltage.

On March 17, 2014 at 11:07am
Mihir wrote:

Heys guys awesome information.
Im in a problem and i need help. my iphone 5 is dead due to low battery and didnt start after that.
i have taken out my iphone 5 Li-ion Polymer Battery and i want some way to externally charge it before putting it back on in the iphone. i basically want to check if its the battery or charging port issue. plz help !!!! thanks.

On March 18, 2014 at 1:44pm
Vince wrote:

@Mihir, you can use an external, stand alone charger to charge the battery outside of the phone.  You can either get one specifically made for your particular battery, or use a universal one.  I bought the PPUCLIP by Lenmar.  You can get it here:  http://www.amazon.com/PPUCLIP-Universal-Charger-Adjustable-Contacts/dp/B001RGYZJS
You can just use a voltmeter to see how much voltage there is in the battery. 

If the PPUCLIP will charge the battery, but you phone won’t, then it’s a bad phone.  If the PPUCLIP won’t charge the battery, then it’s a bad battery.

On March 18, 2014 at 2:15pm
Vince wrote:

@peteypablo, I don’t think it really makes any difference if you do 85/35 vs 75/25.  Just make sure you giver her enough juice to make it through the day.

As for the long term damage, no matter what you do, you’re always doing long term damage.  That’s why they will eventually die, no matter what you do.  It’s just a matter of trying to do the least damage possible. 

But as for catastrophic sudden damage, you can run the battery all the way down until the phone shuts off, and it will be fine.  The battery itself has a protection chip in it to prevent it from being discharged below a level it could be recharged from.  I let mine die all the way sometimes.  I carry an extra battery or two in case I need them.

On March 30, 2014 at 6:59pm
diggler wrote:

Started reading post then saw how many there were so decided to ask my question and comment instead of reading the hole list.

Comment- I’d love to see “Figure 3” charging to 4.1v instead of 4.2.

Question- Although a saturation charge put’s more stress on Li ion cells at 4.2 providing a little more capacity but shortening life cycles. Does the same thing apply when allowing a saturation charge at 4.1v?

Also is there any chargers on the market that will allow you charge to 4.1 or 4.05v then stop charging once the battery voltage has caught up? Indicating saturation charge has started. Or are you just supposed to sit there with your volt meter?

A hi voltage alarm would work hooked to the battery. Is there such a thing? Iv only seen low voltage alarms. hmmm…. need to do more research.

On April 5, 2014 at 5:00pm
Kathy wrote:

I purchased a flashlight that came with a battery and charger and it said to charge for 8-10 hours before initial use.  I put it in the charger and about 12 hours later I remembered it.  This is a 18650 battery.  I put it in the flashlight and the flashlight didn’t work properly.  As I screwed on the end cap the light was bright but as the cap was tightened it seemed to affect the flashlight into not working or working sporadically.  I don’t know what to do at this point ... looking for advice.  Do I need a new battery now?  New charger and battery?  New flashlight also?  I am tempted to return it to the store now, I am sad and wonder if it should have still worked or if I ruined it. ?

On April 5, 2014 at 11:40pm
Khairul wrote:

Hi all,

I have a phone whose original battery is Lithium-Ion 3.7V 1150mAh. The charger that came with the phone had an output of of 5.25V 60mA. Unfortunately I have lost the original charger but I do have spare charger whose output is 5V 1A.

Being a noob when it comes to stuff like this, can somebody tell me if using my spare charger to charge the original battery would reduce the battery’s life in any way? Or would I be better off buying a manufacturer-approved one?

On April 5, 2014 at 11:42pm
Khairul wrote:

Obviously I made a bit of a typo in my post above. It was of course meant to be 600mA, not 60mA. I’d be grateful for a quick response.

On April 14, 2014 at 11:40pm
naga raju m wrote:

How to decide time out value according to temperature.
How to check Battery open condition, What is Battery open condition normally.

On April 29, 2014 at 6:12am
kerollos wrote:

My.xperia z1 compact charge at 4.35 v is it harmful?

On May 9, 2014 at 7:25am
peteypablo wrote:


thanks for your reply.

you mentioned before that ideally it be best to charge the battery when it reaches just below 3700mv and stop charging just after it reaches above (which is impractical of course)

as i have a 3000mah battery, what % level of charge is left when it reads 3700mv?

and what does this article say is the best mv to not let it drop below when you start charging again in order to prolong battery life as oppose to run time?

i usually charge at 30% so 3720mv on my extended battery but i feel maybe i can actually let it drop lower as the ideal charge voltage should be lower?

On May 10, 2014 at 8:45am
Chen wrote:

quote: “Before prolonged storage, apply some charge to bring the pack to about half charge.”
But my Canon S90 camera’s manual states that “to store the battery for long periods, deplete and remove it from camera. Storing for long period without depleting, may shorten its life.” (The camera shipped with a NB-6L 3.7V 1000mAh Li-ion battery)

So I’m really confused. Whom should I believe, the manufactures’ manual or this article?

On May 10, 2014 at 8:52am
Chen wrote:

quote: “Before prolonged storage, apply some charge to bring the pack to about half charge.”
But my Canon S90 camera’s manual states that “to store the battery for long periods, deplete and remove it from camera. Storing a battery for long peroids without depleting may shortern its life”. (The camera shipped with a Li-ion battery: NB-6L 3.7V 1000mAh)

So I’m really confused. Which should I believe, the manufactures’s manual or this article?

On May 10, 2014 at 8:53am
Chen wrote:

quote: “Before prolonged storage, apply some charge to bring the pack to about half charge.”
But my Canon S90 camera’s manual states that “to store the battery for long periods, deplete and remove it from camera. Storing a battery for long peroids without depleting may shortern its life”. (The camera shipped with a Li-ion battery - NB-6L 3.7V 1000mAh)

So I’m really confused. Which should I believe, the manufactures’s manual or this article?

On May 10, 2014 at 9:00am
Chen wrote:

quote: “Before prolonged storage, apply some charge to bring the pack to about half charge.”

But my Canon S90 camera’s manual states that “to store the battery for long periods, deplete and remove it from camera. Storing a battery for long peroids without depleting may shortern its life”. (The camera shipped with a Li-ion battery - NB-6L 3.7V 1000mAh)

So I’m really confused. Which should I believe, the manufactures’s manual or this article?

On June 3, 2014 at 9:03am
Prowse! wrote:

“On December 2, 2010 at 1:12am
Steve Webert wrote:
Does it benefit a lithium-ion or lithium-ion-polymer battery to periodically discharge it “fully” (ie, down to the above me”.ntioned 2.7V-3.0V range)?
I have read several OEM’s offering differing strategies for optimizing battery life.
Thank you for your time and efforts—I very much appreciate the above instruction.”

DUDE, what the hell!? READ THE ARTICLE. NEVER ever ever, NEVER let a LI-Ion get anywhere near below 3.0v for any period of time, to do so renders your battery useless.  3.2v to any device, means ZERO, “I turn myself off now, no matter what, thankyou for using me”. (That’s the device talkin’, yo!)


On June 18, 2014 at 2:44am
CAMPOS wrote:


I have a battery 1S4P Li-Ion 3.7V 8800 mAh (4 cells of 2200 mAh in parallel). I have a station charger model ELV ALC8500 Expert 2.

I have charged the battery yesterday in conditions C/2 in CC ( Constant Current step, 4.4 Amps of charge current), then max voltage when CV step (Constant Voltage) equals to 4.2 V. I have started the charge, then stopped it as needed to get back to home. When I stopped it, it was entered in the CV step, but wasn’t finished (not yet arrived to 0.03 Capacity conditions) . I wanted to restart the process this morning, to finish the charge, but impossible. When i read the voltage, it is indicated 1.8 V, meaning the battery is dead. I really don’t understand what happened. The battery was disconnected, in a closed plastic box, with good temperature.

Does someone has ever met this case?

On June 18, 2014 at 5:27am
Andre Van den Wyngaert wrote:

seems to me this is a flashlight problem, not a battery problem. The light works when you unscrew the cap a little bit. I think your battery and charger are OK. Maybe tightening the cap puts too much pressure on parts inside the flashlight.

On June 18, 2014 at 5:32am
Andre Van den Wyngaert wrote:

your new mains adapter has 5V instead of 5.25V. So it won’t harm the battery or the charger circuit inside the phone. Worst case, your battery won’t get fully charged or won’t charge at all if 5V is too low for the charger circuit. Your max adapter current 1 amp is no problem. The phone will never draw that much out of it, so you have some spare.

On July 9, 2014 at 1:54pm
peteypablo wrote:


I was hoping you might be able to shed some light on this battery situation I’m having, judging by the information above in the article temperature makes a huge long term impact on battery life i.e. above 30C is detrimental.

it’s summer here where i am and even though the temperature is only 20C in my phone the battery temperature is usually in low to mid 30C’s (unavoidable really, even in an indoor air con place) and i’ve noticed a dramatic drop in my battery life judging by the voltage.

a few questions I have is.. if the temperature is high therefore i’ve lost overall capacity in the past 2 months.. ie usually i charge at 30% with the voltage reading higher than 3795mv and above.. but recently i’ve looked at the battery info at 30% it now says 3700mv or below.. im using same charger charging same way the charger which came with the device.. would it be plausible that the heat has reduced my overall battery capacity?

something you mentioned before that the speed at which the charger chargers the phone affects how much voltage reading there is.. i.e. if it fasts charge with the charger then obviously the run time wont be as long.. however it’s the same charger charging the same way as before.. is the only explanation that the heat has reduced the capacity overall?

bear in mind i do not charge it to 100% often as it causes stress on the battery so that can be ruled out.. i used to be able to get by around 80% battery but now these days i cant seem to get through a day with that much.. i.e. when i charge again at 30%..

is it plausible that (ruling out that i dont let it drop to zero, always charge at 30% and lowest 16% once in a while) and never charge to above 93% (only once in a while) mainly always take off at 70% cos it takes so long to charge i get impatient.. that effectively my battery capacity has reduced dramatically?

i only got it in march manufacture date was jan 2014 and it’s only been warmer the past 2 months and that’s when i’ve noticed the dramatic reduction.. the annoying thing is there’s nothing i can do as there’s no fan to keep it cool, i already keep the case slightly open to let the hot air escape.. and also it’s incovenient being unable to use the phone when there isnt a fan source.

is that probably the most likely explanation? it seems due to the higher temps i’ve lost 10% overall battery capacity (assuming the reading is correct and it is not charging faster than normal)

consequently.. if the overall capacity reduces does that therefore mean the phone should charge quicker to reach 80%? i assume that’s how i’d know if the capacity has been reduced noticeably.

On July 10, 2014 at 12:49am
Andre Van den Wyngaert wrote:

you cannot destroy such a battery with the standard charger, even if you leave it in for 24 hours. The problem you have must be with the flashlight itself. I hope they didn’t tell you otherwise in the shop…

On July 15, 2014 at 6:32am
Oliver wrote:

Hello guys
I have carefully studied this website about lithium ion batteries, i wanted to know if hd gaming on smartphones reduces battery life since high demand gaming applies high currents to the battery (usually more than its nominal capacity) and very rapidly drains it. does it highly affect cycle life? should i stop playing high quality games on my smartphone?
thanks in advance,

On July 23, 2014 at 10:16am
Shahid wrote:

I want to ask a basic question about charging process of multiple batteries at same time…

For example if I have connected some lithium cells of 4v in 5s3p…
Now if I used them 50% then after start charging the whole circuit with one charger what happened?
Do they get charged one by one in a circuit or all will charged at once with same voltage increment…?

thanks in advance

On July 26, 2014 at 2:24pm
Hashaam Sayed wrote:

Hey sir i need your help!!AS i am using a phone now a days (sky vega 850) and it’s battery is Li-Ion 2600 mAh battery now i lost mine original charger now can you guide me which type of or i should say which type charger that contain how much ampere should i used…i need your comment as i am little bit worried about my phone

On August 2, 2014 at 11:45pm

please someone give correct info about using new lithium ion battery for the first time.
i am very confused about this as everyone has different opinions

On August 20, 2014 at 12:12pm
José wrote:

My mobile is a Cynus E1 (Mobistel), has little time and I’ve noticed that the percentage that tells me to be on the percentage is different when I turn it off to charge. Arriving at 15% I turn it off, I connect and gives me a 50% !! . Not always gives me these incorrect percentages. I’ve calibrated following the steps of the video, by the way, excellent video and for several days it looked like it had been solved. I usually do not complete charge and discharge. I usually do loads of different percentages, 44%, 60%, 15%. according to the occasion. That if the phone does not turn off but it has me a little worried. I have entered into some forums and there are people with the same problema.Mi question is: Will faulty battery, has a solution ??. Thank you

On August 20, 2014 at 1:42pm
Damian Donca wrote:

How can I calibrate a smart phone battery?

On August 21, 2014 at 9:48am
Aja Berger wrote:

Can a 12 volt lithium ion rechargeable battery be used to charge the 3.7 volt battery in a cell phone?

On August 27, 2014 at 6:18pm
Ashish wrote:

I bought a new li-ion battery for my smartphone xolo q1000 it was well charging on the 1st day but the next day how much ever I charge its not charging at all ..why is this??

On September 7, 2014 at 9:31pm
Adalb wrote:

Will frequent interrupted charging of phones (or so) affect its Lithium-Ions ? Let us consider this constantly repeated cycle : 20 s of charging + 60 s of pause for a half day ...

On September 7, 2014 at 9:36pm
Adalb wrote:


What if I charge my Iphone in an interrupted way ?
Let’s consider this pattern: 20 seconds of charging and 60 seconds of pause. All this for a half day or so.
Will that affect the battery ?

On September 9, 2014 at 4:46am
Gary Stackaruk wrote:

I have purchased Lithium PO4 batteries. Each battery is rated at (3v-3.2v-3.65v) 20Ah-60w
What would be my charging v outputs from 60 to 85%?

Thanks, Gary

PS- The BMS is the Ligoo & the Battery pack will be a 400Ah. The charger is a TCCH-4k
input is 240 @ 8.1 amps

On September 23, 2014 at 2:32am
Haresh prajapati wrote:

i am design a AC to DC charger for Usb devices . And i am some query about that. My requirement is the when only device is connected then and then charge otherwise this circuit is off. in short i want to save a power when the device is not connected

On September 23, 2014 at 2:43am
Haresh prajapati wrote:

hello to all of you
i am design a AC to DC charger for the usb devices. so in this when devices(load) is connected then and then charger is work otherwise not work. In short i am saving a enrgy is it possible ????
If it is possible then which circuit is used for the load detector ???????

On September 23, 2014 at 8:43pm
Dean wrote:

Why would a charger drain a battery pack?

On September 27, 2014 at 5:07am
peter d wrote:

I have a cycle light supplied with a 8.4 volt 6400mAh battery pack. the supplied charger has an output voltage of 4.2 volts at 500 mA. the battery refuses to charge - am I missing something or is it obvious. I am a graduate electrical engineer

On September 28, 2014 at 5:41am
Siddhant wrote:

I have purchased a new lithium ion power bank. There is some partial charge that it came with. Should I first discharge the battery completely and then charge it fully or should I first charge it completely and then start using?

On October 17, 2014 at 6:07am
noelle morris wrote:

idn’t know that my phone was like 40% then when i got on the bus it was 90% aka this is from 10- 17-14 i am ijn 6th grade btw

On October 20, 2014 at 2:37am
Yam wrote:

Merci et bravo pour ces informations très claires.

On November 14, 2014 at 9:46pm
Lovey wrote:

I have LG G2 mobile phone purchases from korea.
My battery removable Li ion of 2610 mah.
My mobile battery is not working properly from last many days.
Many time i used data cable for charging my mobile.
I have 1.0 Amp mobile charger, Please tell me what is the right procedure to charge my mobile.
Please tell in steps.
I want to change my charger by 1.5 amp or 2.0 amp. Which one is good for my mobile battery.

On November 19, 2014 at 1:26am
Nikhilesh Mishra wrote:

As stated in the article its best not to fully charge and fully discharge the battery which is very much known fact and logical, so I want to charge my 4.35V LG D1 (3000 mAh) cell to only 4.1V. I want to know should I just charge it to 4.1V in constant current mode and then disconnect the charger, or should I charge it to 4.1V in constant current mode and then keep 4.1V in constant voltage mode till charging current tapers to a small value?
What is better for cell? Is there any advantage or drawback of any method?

On November 19, 2014 at 1:28am
Nikhilesh Mishra wrote:

As stated in the article its best not to fully charge and fully discharge the battery which is very much known fact and logical, so I want to charge my 4.35V LG D1 (3000 mAh) cell to only 4.1V. I want to know should I just charge it to 4.1V in constant current mode and then disconnect the charger, or should I charge it to 4.1V in constant current mode and then keep 4.1V in constant voltage mode till charging current tapers to a small value?
What is better for cell? Is there any advantage or drawback of any method?

On November 19, 2014 at 1:08pm
JohnS wrote:

I am interested in buying Li-ion 9v batteries but was taken aback by the large numbers of Amazon users that ended up with dead batteries from allowing the voltage to drop too low.  I come across this all the time with NiMH batteries with my expensive charger where the voltage is too low to register with the charger, so it never initiates a charging-cycle.  The solution is just to stick the ‘dead’ battery on a cheap charger that always supplies a constant voltage supply and the battery soon comes back to life!

I figured this was the case with Li-ion batteries also - until I came across this article!  This piqued my interest enough to dig out a few brand-new but very old mobile phone Li-polymer batteries I have - over 8 years old but never used & still enclosed in their plastic shrouds.  Sure enough, the measured battery voltage was zero.  Setting my bench power supply to 4.2v and limiting the current to 100mA, I connected up the ‘dead’ battery and straight away it started to charge!  It has been charging for several hours now, the voltage across it slowly increasing (it’s about 3.9v now)  - due to the power supply’s current-limiting - and I have no doubt that I will end up with a fully charged Li-ion battery.

So I don’t know what to make of this article now - or the scores of Amazon buyers that have ended up with ‘dead’ batteries…

On December 1, 2014 at 7:06am
JOMIT JOY wrote:

i want to know
what will happen if a LI-ion battery continuously charged without unplug the charger??

also what happen if the battery charged and use for some time & again charged after some time without discharge the battery to the minimum charge(not only one day,all times doing this ) so any problem??

On December 1, 2014 at 11:53am
Nikhilesh wrote:

1. what will happen if a LI-ion battery continuously charged without unplug the charger??
Even if you have continuously connected the charger the charger is smart enough to not to charge the battery once its fully charged. There is nothing wrong in keeping battery always connected to charger. Infact laptops which are being used in home are almost always connected to charger. the only harm is that Lithium batteries don’t like highest and lowest allowed voltage level. So even its safe to constantly keep the battery at full charge the rate of deterioration of battery is higher compared to keeping the battery at about 40% charged. But then its not possible to maintain the battery charged to 40%.

2. What happen if the battery charged and use for some…....
There is absolutely no problem in doing that every time. In-fact it will increase your battery life. Remember cells dont like extreme high or extreme low voltage. Only problem is that the state of charge (SOC) calculator will slowly drift away and will show you wrong capacity remaining values. They correct themselves each time the highest and lowest voltage level are reached.

On December 6, 2014 at 8:32am
Battery Bro wrote:

One thing to note… the article states

“Manufacturers recommend charging the 18650 cell at 0.8C or less. “

Actually manufacturers require charging the 18650 cell ABOVE zero degrees Celsius. The 0.8C is a simple a way of to talk about charge and discharge rates for batteries.

On December 6, 2014 at 10:04am
Ottavio wrote:

How to charge Li-Ion 3.7V?
I’ve a iMAX B6 Pro charger that assumes Li-Ion cells have a nominal voltage of 3.6V and Li-Po have a nominal voltage of 3.7V.
I’m going to charge some 18650 cells taken out form some laptop battery pack. They are marked as Li.Ion but with a nominal voltage of 3.7V.
Now, how should set my charger? According to the chemistry (Li-Ion 3.6V) or to the nominal voltage (Li-Po 3.7V) In the firs case i’m afraid to charge the cells not completely, in the second case i’m afraid to overcharge the cells with the risk of fire.
Please help me to understand what to do.
Thank u very much!

On December 8, 2014 at 10:46am
JohnS wrote:

Well caught battery Bro!  I am now wondering just how ‘authoritative’ this article really is if the author actually believes that the manufacturers are referring to temperature!  This is a real rookie-mistake to make.

On December 8, 2014 at 12:26pm
Brad T wrote:

RE: “Manufacturers recommend charging the 18650 cell at 0.8C or less. “

“C” in the article refers to a unit of measure based on the capacity of a given battery. A 1000mah battery would have a C rate of 1000ma

eg 1 C = 1000ma, .5C = 500ma

The following statement involving temperature is has no relation to the C rates.

On December 9, 2014 at 10:59am
JohnS wrote:

Brad T, that post of yours is really opaque - on the one hand you seem to agree that the reference to C has nothing to do with degrees Celsius and actually refers to battery capacity.  but then you write;

“The following statement involving temperature is has no relation to the C rates.”

- which is meaningless, if only because nothing follows that line!  Or was that line meant to read “The following statement involves temperature and has no relation to the C rates.” ???  Either way, nothing followed…

On December 9, 2014 at 11:12am
Brad T wrote:

My comment was only to suggest that “C” (when referring to C-Rate) was possibly being confused with degrees Celsius only because the writer refereed to temperature directly following the statement about C-Rate.

Anyways… I think I just added to any confusion that may have been present in the comment discussion.

On December 9, 2014 at 6:44pm
JohnS wrote:

Thanks for the clarification.

I may as well take the opportunity to add a note on the Li-polymer batteries I was playing with that mentioned in my first post.

The brand-new (8 year-old!) battery when left charging overnight on 4.2v @ 100mA was drawing zero current next day, so fully charged.  I stuck it on a small 12v motor that draws at least 100mA, which continued to spin for at least 11 hours - so the battery would have delivered its full rated capacity of 1260mAh.  Having done this a few times now with 2 of these same batteries, one a well-used one from an old mobile phone, what is immediately obvious is that protection-circuitry is built into these batteries - when the voltage drops to 2.50v, it is switched off completely, dropping to zero volts.  This to me reaffirms how crucial it is with Li-batteries that the voltage should not fall below this.  I am also very impressed that even after sitting for over 8 years, these Li-polymer batteries both immediately accept a charge, and deliver their rated-capacity back to a load.  I also have (many) 3.6v NiMH batteries of the same age.  While most were also brand-new then, many have ‘leaked’ badly in the interim.  The ones I tested did take a charge though, and delivered close to their rated capacity.  However, their being charged only exacerbated the leakage problem, which they continued to do even after several charge/discharge cycles.

So, personally I think Li-batteries are a far better technology than NiMH, especially long-term.

On December 16, 2014 at 7:53am
Rajesh wrote:

I had buied new li-on battery i does not charge my battery up to full charge now it works up to 1hrs

On December 28, 2014 at 3:54am
James wrote:

I am now trying to design a Li ion battery charger and facing 2 questions about charging a Li ion battery.

1. Is there any maximum charging supply voltage for charging the battery? It seems that it is dangerous if I apply 10V to charge the 4.2V battery. Or should we only focus on the charging current?
2. The paragraph states that the maximum voltage of most of the Li ion batteries is 4.2V. How can we measure voltage when we charge the battery? The battery emf ( that means the open circuit voltage) to voltage across the 2 terminal.

On January 4, 2015 at 2:59pm
Jerry Jones wrote:

Apple suggests to fully cycle (fully discharge/fully charge) its batteries once per month. This suggestion seems to fly in the face of the points made in this article. Who’s right?

On January 4, 2015 at 10:48pm
Ryan Evans wrote:

Is charging the battery fully in a battery charger better than charging it in the phone or worse or about the same?

On January 8, 2015 at 7:25pm
Nancy wrote:

I bought my camera with 3.6 v lithium ion battery in Korea. I will be moving back to Canada. Can I charge these batteries in a Canadian charger that I will purchase when I arrive home? If not, do you thnk the camera will function the same with the same type of battery bought in Canada?

On January 12, 2015 at 2:30am
petey pablo wrote:


I recently got a tablet with a 9500mah battery I also still have my phone with 3000mah and a spare with 2100mah.my confusion is that I followed your advice to charge it when it drops below 3700mv which is around 25% on my 3000mah battery and 32% on my 2100mah one.

My confusion is that on the massive 9500mah tablet battery it reaches 3700mv at only 45% battery??? Why is that..is it a calibration issue?

On January 19, 2015 at 6:41am
Ankit wrote:

i hav moto x 2013 which has a 2200 mah li-ion battery ..
i usually charge it upto 100% the use it till 1% ans repeat the process every day
after reading this matter above ,i am confused
can any1 help me by telling how to charge it ..i mean frm what % till what %

On February 1, 2015 at 7:16am
danimal wrote:

i’ve heard you may be able to recover a “dead” lithium cell by charging it with very low mA, like 10-20 mA until it comes back up to around 1-1.5 volts.

can this be achieved by hooking up a 1.5 volt alkaline battery (or several) into them?  if so, how do you calculate mathematically, how many mA the aa/aaa battery will shoot into them

On February 1, 2015 at 10:09am
James wrote:

Does all of the information contained in the original post still apply?  I’m thinking that battery technology may have changed and improved since it was written.

On February 25, 2015 at 1:34pm
Kenny wrote:

Here are some answers that I believe are correct:
12/28: James: It would be dangerous to apply voltages greater than 4.2V.  I would focus on the charging current, and limit it to 0.8C max.  I agree that it is difficult to measure the battery voltage while charging.  Even though the internal resistance of the battery is low, the voltage will still be elevated slightly compared to the actual voltage of the battery.
1/4: Jerry Jones: Apple suggests doing a full discharge/full charge cycle once a month to calibrate the percentage of battery life indicator.  This process will shorten the overall life of the battery, but once a month should not affect it significantly.
1/4 Ryan Evans: About the same for charging in a phone vs. a charger, depending on the charger.  However, in a phone that is still powered on, that may be a little worse since the charge circuitry could get confused with the power draw from the phone. So maybe the separate battery charger (if it’s a decent one with proper voltage control) would be slightly better.
1/8: Nancy: The country of the charger shouldn’t make a difference so long as the outputs are correct.  Just make sure that the output voltage of the chargers match.  The country of the batteries shouldn’t matter either, so long as they are the same type.
1/12: petey pablo: Unfortunately, I don’t see any answers from Vince here for a while.  I agree that the difference in the percentage of run time reading is a calibration issue.  The discharge voltage for Li-ion batteries are fairly flat around the 3.7V range, so a very slight difference in voltage could translate to a significant percent of run time difference.
1/19: Ankit: Charging to 100% and discharging to 1% is stressful to the battery, and will shorten the overall life of the battery, but it will (obviously) give the longest time before recharging is necessary.  If you can, I would charge from 80%-20% to prolong the overall life of the battery.  Even reducing the span to 90%-10% would help. Most people care more about how long their phone run between recharging since they change phones (or batteries) once performance drops.
2/1: danimal: The amount of current flow follows Ohm’s law, I=V/R, where I is current in amps, V is voltage difference between the source and destination batteries in volts, and R is the resistance in the circuit (both internal to the batteries and external to the batteries) in ohms.  You will need a series resistor in the charge path since the internal resistance of batteries is typically very low.  The resistor would be R=(Vs-Vd)/I where Vs is the voltage on the source battery, Vd the voltage on the dead Li-ion battery, and I = 0.01A to 0.02A.  This is assuming that the internal resistances are small.
2/1: James: good point.  I think that this article refers to the most common Li-ion battery formula, Lithium Cobalt Oxide(LiCoO2).  I believe that the basics still apply to other Li-ion technology (don’t operate continuously at full charge, don’t fully discharge) but the specifics (charge voltage, max voltage, charge current) may vary.

Hope that you all check back to see these answers!

On February 27, 2015 at 12:51pm
Christian wrote:

Hello guys, I’m buying a smartphone that does not bring original charger. The battery is 2400mAh li-ion. I wonder how many amps have to take the charger to extend the useful life of the battery, if low amp (500mA, for example), or a high amperage (1A-2A). How many amps should I buy?


On February 27, 2015 at 3:06pm
Kenny wrote:

@Christian: For a 2400mAh, the 1C rate is 2.4A. The maximum recommended charge rate is usually 0.8C, or 1.92A.  So I would not use anything greater than 1.5A just to keep a little margin.  After that, it’s just how fast you want to recharge your battery.  At 1.5A, the battery will recharge in less than 2 hours.  500mA will take ~5 hours for a depleted battery.

On March 5, 2015 at 6:46am
mert wrote:

i have a 3.7 v. li-on battery 900mAh 3.33Wh
how many hours do i have to do the first charge of it ?


On March 6, 2015 at 8:15am
DJ wrote:

can I charge a 18650 to 4.2V even though it’s a 3.7V 2500mAh?

On March 18, 2015 at 12:25pm
Christian wrote:

Guys, for a 1430mAh battery li-ion, is recommended a charger with 500mAh max? or is possible 1A?

On April 8, 2015 at 9:49pm
Mina wrote:

Should i make sure that mysamsung tab4 baterry fully empty then recharge it or is it ok to charge it even if its not fully empty. Thank you.

On May 2, 2015 at 7:17pm
tim wrote:

Hello B.U. / kenny,

I have a device (portable amplifier) that claims to use a 4-pack li-ion. The original charger of that device is a 3P10-L1016. Output: 16.8V 0.45A. My question is, can I use the same model 3P10-L1016 but with a different amperage? The replacement charger I found has rated output of 16.8V 0.6A

I really need help on this as I don’t want to make a mistake and destroy the amplifier. Thank you!

On May 19, 2015 at 2:54am
Martin Butcher wrote:

More a query than a comment. I am currently living in Malawi where there has been a variety of programs providing solar panels in villages. Somebody with electricity can charge about 10cents to charge a phone, however I have just heard that people are avoiding getting their phones charged with those that have solar power on the grounds that solar charging reduces the lifespan of the phone battery. Does this sound realistic, or might it be a myth? ( possibly promoted by those who are wealthier and have mains electricity connection)

On May 23, 2015 at 2:29pm
Vincent Aquilina wrote:

Very detailed explanations. I have built a few Charging systems myself and the information you supplied gives a good insight on do’s and don’ts. Thanks

On May 24, 2015 at 7:39pm
tom wrote:

ijust bought a 9000 mill amp battery pack for my phone it had no charge when it came out of the box charging with a 2.1 amp charger it charged a bit quicker then expected but its charging so this battery can only get a slow charge due to the limits of USB but would a 1 amp charger be better for longer life or would it not matter

On June 2, 2015 at 6:51pm
Kenny wrote:

Sorry, haven’t checked here in a while.  Here are some answers that I have:
3/5: mert: The time to charge depends on the amount of current your charger can provide, and the initial state of your batteries.  Li-ion batteries should be shipped with 40-60% charge.  Assuming that your batteries are about 3.7V to start, then the charge time will be about 1 hour at 500mA, or 1/2 hour at 1Amp.
3/6: DJ: Yes, the 3.7V is just a nominal voltage for a Li-ion battery.  Charge at 4.2V for a full 100% charge
3/18: Christian: Max charge rate is usually 1C, or 1.43A for your battery. Recommended charge rate is 0.8C or 1.144A.  So for a fast charge, you can use 1A max.  500mA would take longer, but may be a bit better/safer.
4/8: Mina: I assume that your tablet has a Li-ion battery.  For maximum life, start recharging at 20% and stop at 80% for maximum life.  Thus, it’s OK (and better for the battery) to recharge before it is fully empty
5/2: tim: Sorry, that’s not quite enough information.  The battery pack capacity rating (in amp-hours) is needed to determine the recommended charge rate.  If the pack is rated for 0.75AH (or 750mAh) then the 0.6A charger should be OK.  I suspect that it will be fine, as most packs are designed to have larger capacity.
5/19: Martin Butcher: Sounds like a myth, but it depends.  If the solar power is converted into standard AC voltage and the phones are charged with a regular charger, then it shouldn’t affect the life of the phone battery any more than regular power would.  If the solar power is fed directly into the phone without regulation, and the voltage varies, then it could reduce the life of the batteries (or more likely damage the phone).
5/24: tom: With a 9000mAh pack, the charge rate of USB vs. 1A vs. 2.1A should not affect the battery life at all, the max recommended rate of 0.8C is 7.2A!  It must take a really long time for a full charge using a USB port though!

On June 8, 2015 at 2:47pm
Richard Cox wrote:

I have read everything I could find on charging LiPos, but there has been no discussion about the charging efficiency, i.e., what percentage of energy put into a cell goes toward actual capacity?  I know that lead acid is about 80%.

On June 10, 2015 at 9:58am
Danigar wrote:

Hi there! You say “A device should be turned off while charging. This allows the battery to reach the threshold voltage unhindered and reach a low saturation current when full. A parasitic load confuses the charger.”

Could you be more specific as to how important this is? Turning the cell phone off and on every time you charge it is cumbersome, so unless it has a considerable impact on battery life I would rather not do it.

On June 10, 2015 at 6:34pm
Tam wrote:

Hey guys, I’m currently using a Li-Ion charger IC(MCP73861) to charge an old 18650. I have set the charging voltage at the “saturation charge stage” to 4.2V but the battery voltage seems linger at around 3.9V on my oscilloscope/data logger.
I know that an old battery may result in reduced capacity but can the same be said for the voltage?

On June 24, 2015 at 2:28pm
peri wrote:

I really like your page. I want to ask where can I find a catalogue with the discharge characteristics depend on time. I have looked everywhere, but I can only find for lead acid.
thank you and congrats for your work.

On July 6, 2015 at 2:34pm
roya wrote:

I`m working on solid electrolyte using Graphite as anode and LiCo2 as anode. My battery does not provide a reliable Constant current charge/discharge cycle. it takes less than a minute to charge the battery to 4.2 v at constant current rate of 0.2 mA and also very short time of around 10 seconds to discharge it from 4.2 V to almost 3v . However, the constant voltage charging process period ranges from 1 hour to 2 hours which means the battery hits the saturation voltage. my question is what can possibly contribute to unsuccessful constant current Ch/D-Ch cycles?

On July 15, 2015 at 4:02pm
Robert wrote:

Does a lithium battery used in a golf cart need to be horizontal for charging or is vertical ok.(the space where I store the cart needs to have it vertical)

On July 27, 2015 at 4:25pm
Kram wrote:

Hreat article, very informative. Thanks!

On July 28, 2015 at 6:19am
Pushpendra wrote:

Hi there,

I have two questions , if anybody can help me to understand:

1. Why we use Cu for anode and Al for cathode as current collector ?

2. how to select a voltage window for a full cell (Li-ion case) while using different anode. Suppose if I am working with Graphite half cell/anode the voltage window to test the battery is 0.0-to 1.5 V. Now if I have a Full cell with LFP/LMO/LCO as cathode and Graphite or Si or LTO as anode than how to select a voltage window to test the battery ?? 

If anybody there can help ?

On August 24, 2015 at 8:01am
Abraham wrote:


I have a battery that i use to charge it with a 10W panel.
the BATTERY IS 3.5 fully charged, a lithium ion battery. nut what makes it a dead battery?? when it turns to 1.0v?? when i recharge it with the panel it turns 3.5v and i can use it again.!!!

On September 16, 2015 at 8:03am
Xasey Godspeed wrote:

Hello everyone
I manage a small wireless business in south Fl
I hav been following an excellent way of charging Li-ion batteries and passing it over to my clients.
>>>.  Lithium-ion Batteries Should be turned off & charged Up to 5 hours before their first use.
• Ignore the phone or dock charger telling you that the battery is Full—this is Normal but, is not accurate if the battery is not initialized.
• Battery life varies by use and configuration.
• DO NOT fully discharge a lithium-ion battery! Below 8-10%  Unlike Ni-Cad batteries, Lithium-ion batteries life is shortened every time fully discharge them. Instead, charge them when the battery meter shows one bar left. Lithium-ion batteries, like most rechargeable batteries, have a set number of charge in them.
•  ONCE INITIALING YOUR BATTERY:  BASIC Handset Within 2 Hrs MAX.  OR   SMART Handset   Within 3 Hrs
a partial charge is better. *  OVER 3 Hrs & OVERNIGHT CHARGING, Talking, Playing while Charging WILL DAMAGE YOUR BATTERY CELLS.

And they work Awesome- Hope will work for you as well




On September 26, 2015 at 7:53am
Stefan Andersson wrote:

Hello guys, just charge the battery when its empty. Good luck charging.

On October 1, 2015 at 4:30am
Vivek wrote:

How to charge lithium ion battery to maximize its life

On October 27, 2015 at 9:48pm
Pouya Parsaie wrote:

I recently download an app which I think could be really beneficial for lithium-ion batteries in mobile phones! This app called ace charge, it disconnect the charge on 100% full charge or even can define to not charge the phone over 80%!

On November 1, 2015 at 4:44am
K B D Prasadrao wrote:

really a good informative and educative article i have gone trough it really gave real picture of the LI-ion batteries and charging modes thank you

On November 2, 2015 at 4:59am
Taxiarchis wrote:

here are my 2 or 3 questions,

1) Is slow charging (via USB-Port) better then fast charging (wall plug)?

2) USB chargers have an output of 5.0V.  Would this cause problems with lithium batteries since as stated above, charging above 4.3v causes plating of the metallic lithium on the anode?

3) I don’t see any comments replied. You reply via email, or don’t? Thanks!

On November 24, 2015 at 7:44pm
Kenny wrote:

I see several unanswered questions.  I can try to answer some of them:
6/8 Richard: Good question.  I haven’t seen any info about charging efficiency for li-ion batteries either.  Post back here if you’ve found any.
6/10 Danigar: Charging while the device is on can full the charging into thinking that the device battery is at a lower voltage than it really is, so I think it matters most when you are near full.  It also depends on how much current the device is using.  That said, I don’t turn off my phone when charging either.
6/10 Tam: Was this after the battery was fully charged (no more current going into the battery)? I think that older batteries will drop in voltage quickly, but should start full.  Not sure why yours doesn’t.
7/6 roya: It sounds to me as if your battery just isn’t holding a charge.  Check for weak/diluted electrolyte?
7/15 Robert: Li-ion batteries can normally be charged in any position - lead-acid and liquid batteries need to be charged upright to allow for potential venting during the charge process.
7/28 Pushpendra: Sorry, don’t know the answer off-hand.
8/24 Abraham: A fully charged Li-ion usually attains ~4.2v when new.  Your battery starts off with a lower voltage which means a shorter life.  It’s not truly dead.  A Li-ion battery at 1.0 volts needs to be recharged, it’s “dead” because it can’t provide much current at that voltage, but recharging it will bring it back to “life”
10/1Vivek: For max battery life, try to keep the charge between 20-80%.  Do not let it discharge completely.  If charged 100%, try to use it immediately.
11/2 Taxiarchis: 1) So long as the fast charge does not exceed 0.8C, it should not damage the battery. Fast charge *might* end up over-charging slightly.  2) The device itself should limit and regulate the charge voltage, so the 5.0V USB voltage is converted to ~4.2V by the device.  If you are feeding the 5.0V straight into the battery, it can overheat and explode.  Some 18650 cells are protected against this, but others are not.  3) I haven’t seen any responses from the author in a long time.

On November 29, 2015 at 6:58am
petey pablo wrote:

Does anyone know what would happen to a new 3000mah mobile battery that was stored in warehouse for 3 months at 1%? Asw we know from here high voltage heat and low voltage ie stored below 5% are very bad for the battery capacity.

Would i notice this issue straighr away?

The battery is sealed in the new phone and cant be removed. How much stress and capacity loss would be caused if such a new battery was stored at 1% for 3 minths?

Are we talking a 10-20% reduction in capacity overall?

It seems fine but im just worried in a couple months it’ll kick in and my battery wont last as long as it does now as i just got the phone.

On December 3, 2015 at 9:20pm
shyam sunder wrote:

Thanks for a superb insight.

Wanted to understand this better so ran some elementary tests

Can you help me interpret the results and answer the questions raised here please http://engineering.stackexchange.com/questions/6406/charging-a-smartphone-battery-while-using-it/6409#6409

On December 10, 2015 at 11:53am
Michael Rosenblum wrote:

This is a great post about Li Ion batteries, and I would like to learn more.
Does anyone reading this post know much about these new Hover Board / Self Balancing Scooters that have rechargeable Li-Ion batteries and have been catching fire or “exploding” during charging or during product use?
These scooters are made primarily in China by a number of different manufacturers, and I’m sure the quality of components and assembly differs.
The more expensive scooters come with Samsung or LG brand Li-Ion batteries.  The cheap ones have Chinese made batteries.
Is a quality battery one of the main contributing factors to prevent the problems of over-heating / fires with these products?
Or is it also a matter of the charging adapter unit that is included?
Do the charging adapters have circuitry inside to prevent overvcharging of the battery?  The ones I have seen have red and green lights. red means charging, green means charged.  Would green light mean that the current from the charger is stopped, because the battery is charged?
Or do the scooter units themselves, or the batteries have built in circuitry to prevent over charging?
I was thinking of buying one of these products for my daughter for Christmas, but would like to knowledgeable about the risks.

On December 13, 2015 at 5:07am
R Krishnan wrote:

Can we Use SOLAR Power to RECHARGE Lithium Bateries.

On December 21, 2015 at 7:27am
Dr Ali wrote:

i bought a Chinese quad-copter phantom 5c from a local store.i charged the battery for 3 hrs but charge-full led never lit. it use to fly for two minutes before emptying the battery .i got its battery replaced from the same store. it came with a usb charger that plugs into wall socket and reads SEC: 3.7v ::: 350mA. the a wire with a usb(and a small circuit on it with a charge=full led) plugs in USB port of charger and other end of wire has a connector that plugs into battery(connector). the new battery reads (ds 852540) 3.7v 650mAh. NOW THE QUESTION IS THAT HOW LONG SHOULD IT TAKE TO FULLY CHARGE THIS BATTERY WITH ABOVE MENTIONED CHARGER

On January 18, 2016 at 3:49am
Ian wrote:

“high capacity Li-ion may go to 4/30V/cell and higher” should be “4.30 V/cell”.

On January 24, 2016 at 8:10am
mohsen.m.shabestari wrote:

i have changed my laptop battery since 6 month ago with a new one it was working very good then amount of the charge reduced to 3/4 of full charge and its about 3 month battery
not charging and condition of the battery are good i have changed the battery with the similar one of my friend it was charging without any problem for your more information my laptop le z500 -45ip lenovo and the battery li-ion color black   voltage 14.4v capacity 2200mAh thanks in advance


On March 2, 2016 at 3:05am
vasu s wrote:

could you any one can tell about how the lithium ion battery full cell making ?
how much cathode(LiCoO2) and how much anode(graphite) we have to take to fabricate the 250 mAh cell…

what parameter i have to take care of when we make full cell…..
the cathode specific capacity 160mAh/g and anode is 370mAh/g ,so that which one we have to considered when we make full cell fabrication….

On March 25, 2016 at 2:46pm
Andy wrote:

If my pair of 18650 batteries become unbalanced how do I get them back to proper balance? They’re LG HG2 3000mah 18650 cells. They’ve been married since day 1.

On April 14, 2016 at 12:42am
Martin wrote:

@ Andy, are they in parallel or in series? In parallel no issue as they will always be balanced. In series you can take them out every 10-25 cycles and charge them separately, if soldered together best is to add a small BMS Battery Monitoring System setup which equalizes the voltages of each cell, depending on how much current is needed the prices vary, some examples, search for 2s BMS 4A on eg. aliexpress.com.

On April 22, 2016 at 1:42pm
Byron Hourmand wrote:

Would a LiPo battery get damaged if after the switch from CC to CV, the CV (4.2V) is not terminated after battery is fully charged?

Your reply is appreciated.

On April 24, 2016 at 12:01pm
Dan wrote:

@Byron Hourmand if you’re thinking about long-term effects, then mostly yes. As it said earlier, lithium batteries don’t like to be neither in a fully discharged state, nor in fully charged. I cannot tell the numbers, but you’re shortening life of a cell while continuously putting it in a fully charged state. This is my 5cents.

(that is the reason why my laptop battery is absolutely dead after 4 years)

On April 25, 2016 at 1:15pm
Byron Hourmand wrote:

@Dan Thank you for the reply!  As you said, there is some shortening of battery life but I haven’t seen any document on how much.

On April 28, 2016 at 11:51pm
Omer YILDIZ wrote:

My question is this:
If I charge Lithium Ion battery non-stop with 10mA, that is 24/7 with no cut, will this damage the battery?
Charging time can be weeks, no problem; my concern is that is this going to damage the battery somehow?

On May 19, 2016 at 4:57am
joe wrote:

yes, it will damage the battery

On June 17, 2016 at 10:53am
Juan wrote:

Hello I have a question what happens if I connect 2 batteries in paralel 1)
500 mAh 3.7 and 2) 400 mAh 3.7 v.  do I obatin more capacity or more or less 900 mAh, or more hours ? Thanks

On July 2, 2016 at 12:44pm
Ron C. wrote:

As long as the batteries “in parallel” are the same chemistry, and (as you state) are about the same capacity, then you can do this, and it will add the capacity ratings. This requires a modification to the charge termination though, as the previous termination point no longer applies with the higher capacity.
More capacity (900mAh vs 500mAh) results in more hours of run-time… that is what “mAh” means… how many milliAmps of load for how many hours.

On July 4, 2016 at 3:25pm
Ian wrote:

The previous termination point of 4.2 V (chemistry dependent) is unchanged.

What’s with the spam posts above? If these comments aren’t moderated at least provide a report option.

On August 23, 2016 at 9:43pm
Vit wrote:

Hello everyone.
I’ve got a question. I have an electric scooter with the lithium ion battery (72V 20Mah). Can I charge it with a charger for lead-acid batteries?

On August 26, 2016 at 7:08am
Bruno wrote:

I’m using a battery pack composed of Li 18650 Cells.
Although the cell data sheet says the maximum battery voltage is 4.2, the BMS manufacturer suggested i define the cell termination voltage to 4,1.
Is there any problem or advantage on this ?
As i see it it will be safer and since i will be working from 85/90 % SOC to 30% it will prolong the batteries life?
Am i right ?


On August 28, 2016 at 9:12am
Jacopx wrote:

It could be a good choice to use battery until 40% of charge then charging it up to 80% and then reuse it? If i’m using the laptop during the charging phase i not good?

Thanks! :D

On September 9, 2016 at 6:35pm
Zhimin Qi wrote:

Get a question, for figure 3. since you first use fixed current then fixed voltage, how to do you calculate the C-rate to be 1C?

On September 22, 2016 at 6:57pm
eric yeo wrote:

I have a battery pack, 6-cell (each cell is 3.7V/2500 mAh) making it to a 22.2V battery pack with protection circuit. I connected to 2 battery pack 22.2V in parallel so that it becomes a 22.2V / 5000 mAh battery pack.
What sort of 22.2V battery charger should I use? There is a choice of:
a) 22.2V / 2Amp battery charger
b) 22.2V / 4Amp battery charger

Can anyone advise?

On October 4, 2016 at 3:33pm
Bernard Schaffler wrote:

I have been commissioned to design and supply the electrical control for a 38 foot electric boat that needs to run silently for 2 hours at 6 knots. The total power required is 70 kW. Light weight batteries is essential. I am assuming Lithium Ion.
I have the ability and experience to produce the intelligent battery charger for lithium ion batteries. Where is the best place to purchase the batteries.

On October 12, 2016 at 4:52am
Glenn Fasnacht wrote:

I am designing a Li-ion charger for a product and will be using a purchased charger IC from a major IC manufacturer. It has the expected precharge, constant current, float voltage phases. I have a limited power source available, so my question is, is there a down side to providing a low current during the constant current phase, like C/20 (other than longer charge time)?

Thanks in advance

On October 27, 2016 at 3:38am
Jeannot wrote:

Thanks for this valuable post

On November 22, 2016 at 5:08pm
petey pablo wrote:

Does anyone know what would happen to a samsung phone which has 3000mah battery but was shipped with 0% battery and subsequently was stored in storage in warehouse for a year and the protection cut off switch was activated so did not turn on upon receiving.

I think the voltage was around 3500mv so 3.5v at 0% maybe a bit less say 3.4v , how much damage to the lithium ion battery would their be if it’s been in storage at low voltage for a year brand new?

Trying to decide whether to send it back. The voltage for my previous phone which i need to send back at 61% battery is 3920mv so 3.92V but on this one (due to damage i suspect of being stored at 0% and sleep switch activated ) at 61% reads 3855mv (3.85V) is the difference of 70mv 0.7V a significant difference?

On November 23, 2016 at 5:58am
petey pablo wrote:

@kenny thanks for your answers hopefully you still respond here or vince.

Following on from my post from a year ago i got another samsung replacement phone unfortunately from same factory which ships the phone with 0% battery. When i received it it would not turn on i had to charge it. I think the reading at 3% was 3500mv so 3.5v. What would you speculate the voltage is at 0% and also when it has switched off itself.

My concern is this 1 was made in December 2015 so nearly a year it has been below 0% and switched off. How much damage is done to the battery long term kept in its sleep mode we are taking at least 8 months.

Even if i get a replacement from samsung or amazon it may be from the same factory which dont charge the batteries before shipping.

Is it elevated self discharge the issue or os it overall capacity?

When i check the reading of my old phone which i need to send back the mv reading at 61% is 3920mv and on this new 1 3855mv ie sbout 70mv lower. Is this due to the storage at less than 0%?

I assume samsung protection switch cuts it off around 3400mv 3.4V and i know letting a battery drop to that low voltage that it switches off is bad even if you charge the next day but if you let it dwell at that in an shut down off by itself state for months how much serious damage is there?

More importantly how do i tell? I have to send back the other one in a week or this 1 and cant decide which to keep. I dont want a battery which will screw up in a few months because some idiots in fsctory didnt charge it before shipping like they are supposed to

Is the biggest issue welf discharge or overall capacity? Reading all the lithium articles it doesnt exactly explain my situation just that if you didcharge to 2.5v frequently ie recharge quickly after the self discharge is only 8mv per day conpared7to 8mv for a new battery. There’s no info on one which has been left in low voltage state of 3.4v then recharged months later.

It only says copper dendrites form below 2.5v and the example they used they shorted the battery but ran it down to 0 volts.

Mine hypothetically shuts off at below 3.5v dependion samsungs protection switch. Would the damage be significant? I can’t replace it it’s non renovable

On January 5, 2017 at 11:26am
Peter wrote:

I have 44 Sinopoly 3.6 volt 200ah Lithium batteries that I have bought slight used, “less than 100 cycles” for an EV project. I am going thru charging and testing them and the BMS that came with them. I have a few questions. I have manged to charge them in blocks of 12 volts with a car charger using the BMS as a shut off. The nature of the BMS is that the charging is shut down when one of the four cells reaches full charge. The temperatures have dropped to -5 to - 9 Celsius this week. Will that effect the ability for the cells to reach a full charge. The reason I ask is I have been charging one cell with a variable power supply that I think has a lower state of charge than others. I have charged it for probably close to 20 hours at about 5 amps and it has not gone much over 3.6 volts. The BMS is set to shut off at about 4.1 the batteries then settle back down to around 3.7 if fully charged. Should I expect the current to drop off if 3.6 volts is all it is going to get to or is it just very low and I need to just keep charging and expect it to rise to the full voltage eventually. The battery is not heating up. What I am wondering is what are the signs of an abused or failing battery in relation to charging. The literature mentions minimum charge rates of 3 percent of capacity is 5 amps enough for a 200ah battery.

On January 5, 2017 at 11:38am
Peter wrote:

As per my previous questions, could I be experiencing some kind of self discharge, given that it is quite cold out perhaps I am not seeing a temperature rise in the cell.

On January 7, 2017 at 6:08am
Dan D wrote:


you may damage your battery if charging in below freezing temp.


Well you get the most of the energy at about 3.6V. If you discharge it and look at the curve - it’s almost flat at 3.7-3.6V.
In my experience dead batteries don’t take charge (or very small amount), sometimes they heat up, sometimes they just take the current and nothing really happens (they neither heat up, nor store the charge). Try charging that battery at normal temp and then discharging. 20h@5A it’s 100Ah, so it should be around 3.6V at half of the charge.

On January 9, 2017 at 2:33pm
Peter wrote:

Thanks Dan for the reply, the temperatures have improved and I think I have given the batteries enough time to charge. All of them have nicely come up to a full charge. I think they were all very badly imbalanced. You are right that zone between 3.6 and 3.7 is huge it takes along time to get to 3.8 at which point it rapidly reaches full charge.
It is a big learning curve getting used to the nature of these batteries.

I have been thinking about charging them in banks of 4 with independent 15 volt chargers and bms shut off. It strikes me that you would achieve better overall balance by managing in banks of four rather than having a single battery in a 32 battery pack determining when to shut down. That said I plan to have independent battery voltage read out’s as well as low voltage cut off.
Any thoughts appreciated as I new to this.

On January 17, 2017 at 7:17am
Fred Becker wrote:


I have 2 devices that have different chargers, one is 5VDC 2 Amps, the other is 5.4VDC 3 Amps.  I’ve been asked to investigate using the higher voltage charger on the lower voltage device.  From what I have read above, it seems there is a risk of the battery exploding/bursting into flames.  I would just like a confirmation that this is correct?

We send these devices out to different customers, and if this is the risk involved we won’t investigate this further.

Thank you.

On January 30, 2017 at 5:53pm
Davidson Duarte wrote:

Please, translate to portuguese Brazil.

On February 5, 2017 at 11:19pm
Sam wrote:

There are much of good information here but please I need help to solve my issue.
I have a RF remote system which is looking for signal at all time.
It has one 18650 Lithium battery.
I need to attach a mini Solar panel (I have a small 5v solar and a DC-DC converter set at 4.1v for charging)
but I do connected this and remove the wire manually.
How can I connect My small Solar panel to the battery and let it be, as I have mentioned the RF system is always working 24/7 listing for signal so the battery last about 6 weeks. how can I accomplish this.
(to have a solar connected to one 18650 battery and solar will be working as long as there is a light and also the system will be draining the battery 24/7).
Thank you ahead for helping me in this matter.
I apologies if I keep repeating this as I have 6 of these systems and it get frustrating to do manual charge.
Thank you,

On February 6, 2017 at 11:41am
Peter wrote:

Fred you definitely need to get a proper charger rated for the battery.You will compromise the battery life and potentially cause other problems documented here and elsewhere.

On February 6, 2017 at 11:51am
Peter wrote:

SAM, You need a simple BMS that will disconnect the solar panel when it reaches the maximum voltage. Look on ebay there are lots of systems out there. You can even get 18650’s with a built in charge chip that I think must shut off the charger when it reaches maximum voltage that might work for you. These 18650’s a slightly longer as a result but might be a good solution for you. Do a search on ebay for “BMS Protection Board for 1 pack 3.7V 18650” you will find it.
Fred this might even work for you to and you would still be able to use the 5 volt charger

On March 23, 2017 at 8:44am
Hiamsnhu mali wrote:

what is the value current for each lithium ion cell?

On April 10, 2017 at 11:05pm
Abi wrote:

I have planned to charge Li-Ion battery using dynamo. Will there be problem if dynamo fails to generate continuous power?

Because dynamo is powered up by hand cranking and it is not possible to crank continuously to generate power. Every 20 secs once cranking will be stopped.

Which means battery will be charged for 20 secs and left free for 5 secs(repeated in regular manner).

Thanks in advance…

On April 22, 2017 at 3:04am
Suman Kumar wrote:

For a 48v lithium ion battery with 3.2v/cell, after SOC 99% to become SOC 100%, why the voltage of some cells crosses 3.8v.
What is the effect of cell voltages at float vltages.

Please suggest.

On May 12, 2017 at 12:55am
Erik Martensson, Sweden wrote:

Question from bike-owner not at all battery-expert:
I have bought the 51913 LION-S battery from SHIDO for my motorcycle BMW R1200CL. Unfortunately on this bike the battery is situated under the petrol tank, so I first have to remove both side covers and the tank before I can reach the battery.
Before buying this Li-Ion battery, I did not know that my “smart” charger from CTEK (with trickle and desulfation mode) is not suitable. But if I have understood the manufactures charging instructions correct, I may use my old common charger that gives 13,2V and max 7A. 

1) Is my old charger appropriate for my battery?
2) I cannot disconnect the battery cables from the bike easily (due to the location), does that prevent me from charging?
3) How do I know for how long time I shall charge my battery? 2-3 hours?
4) If I forget to disconnect the charger, will that damage the battery?

Thank you so much for the answers!

On May 26, 2017 at 3:27am
Costas Mel wrote:

Dear all,

Maybe my question will sound silly but I would like to ask why we have to charge in constant current since we have a balancer?

Kind regards,
Costas Mel

On May 31, 2017 at 9:19am
Kenneth Mordi wrote:

Hi, can someone tell me the best battery type for grid-connected application like MMC battery energy storage system. Is it Lead‐ Acid, NaS, Li‐ion, or Flow Batteries?


On June 4, 2017 at 4:08pm
Artis wrote:

Here is a problem. You can buy cell balancing circuits online (ebay, aliexpress), but why they manufacture these circuit boards with cut-off voltage of 2.4v?

On June 12, 2017 at 4:32am
Prajod k wrote:


Am clarifying the following things.
1) Normal charging current for li ion battery pack is 0.5C to 1C.Right?
2)If we connect the charger which can supply the current of 0.2C, Whether this battery charger can charge this battery pack?

On June 12, 2017 at 11:21am
Suman Kumar wrote:

I am using 15 numbers of 3.2V Li-ion cells to make a 48V battery.
Plz anyone tell that upto how much voltage I need to charge my cell and battery to get 95 to 100% capacity.

On June 22, 2017 at 9:44pm
Felix snow wrote:

Please help
Im bought a music player or DAP(digital audio player) which doesn’t come with charger adapter it only had cable of type-C to USB to charging.i wanna ask some questions
1.if the device need 5V 1A is it good/safe if i using adapter that come with 5V 2A for long term?? I worry it will ruin my battery life
2.which the best method, buy an adapter and charge it with adapter 5V 2A or charge it using high end desktop computer with usb 3.1 which covered with UPS?? For more stable flow which is good to go??
3.could you give me some good an adapter brand for my music player?? I just dont want take a risk for buy cheap adapter because the music player was not cheap and i want it be good as last as possible
Thank you

On June 25, 2017 at 8:37am
Trivet Grunzen wrote:


Your papers on battery technology are brilliant and open.

In the article on Lithium batteries, it implied that as long as the maximum current and maximum voltage for the battery technology were not violated, the charge cycle did not really matter.  Is that correct?  Specifically, irregularly trickle changing should not be a problem, given the voltage and current constraints.

Thank you for your excellent work!

On June 26, 2017 at 2:50am
Jonathan B wrote:

Is it a bad idea to use a phone while charging the battery? Why or why not?

On June 28, 2017 at 8:57am
Ron Haber wrote:

My Android phone’s battery is removable. I have recently bought a second battery, so now I charge one in an external charger while using the other. The problem is that when swapping the batteries Android Marshmallow always shows the same percentage for the new battery as for the old. Therefore, I can never really know what the true percentage is of the new battery. Is there a solution, short of the ridiculous expedient of recalibrating each and every time?

On July 6, 2017 at 6:41pm
LadyKenai wrote:

I am using LI Ion 5800mAh 3.7v batteries for flashlights.  Should I discharge them all the way before recharging them?

On July 10, 2017 at 10:05am
Walter wrote:

Great article. I have been confused for a long time about charging and howbit affects battery life, especially Li-ion batteries, now I have digested this article and I understand how it works. Am glad I found this article.

On August 13, 2017 at 2:28am
Dominik Mayer wrote:

Is the ntc necessary when i want to charge a 3.7 volt 6000 mAh battery

On August 23, 2017 at 8:57am
Alexander wrote:

My colleague read somewhere that the best way to charge battery pack is using current for a single cell. So for 18650 is 0.8C of a max today 3500mAh. Even if a battery pack have configuration 2S6P for example. Is it true? I mean it’ll take too long…

On September 10, 2017 at 10:02am
Tobi wrote:


I am building a small home solar system to store power.  The plan is to be able to use that power on my ebike.  Currently I have 2 52V 13.5ahr lithium ion battery packs for my bike that I switch in and out.

I have purchased some 100W panels as well as an http charge controller. 

My question is should I store the solar energy in a higher capacity batter (or a lead acid) and then charge my lithiums from that battery, and how would I do that safely.

Or can I charge the Lithiums directly from the sun?

On October 6, 2017 at 9:16am
Scott Bagby wrote:

I would like to know if a supply voltage of 4.00 volts is hooked up to a lithium ion battery (4.20 volts 100% SOC), can the 4.00 volts be left on indefinitely? And be safe?  If not, is there a power supply voltage level that would be safe? I.e. - 3.95, 3.90, 3.80, etc.?
The 4.oo volt supply would allow for trickle charging up to 75% SOC and the battery would available for a short term high current draw as required from the battery.

On October 19, 2017 at 9:20am
Fayiz Shaffaq wrote:

Does charging your battery to 80% and discharging it to 50% make it last three times longer than it would if I charged it all the way to 100% and discharge it to 10%? Btw I am not a geek and that is why my peanut brain couldn’t understand the above explanation.

On November 2, 2017 at 9:11am
Nick Ercklentz wrote:

I have a question for a NiMh battery expert. I am building a 22 NiMh battery array and need to know how to charge it quickly and safely. It is going to consist of 22 type NUN 3000s in series (1.3Volt, 3000MaH). I need to know how to best charge these.I am assuming I will need to have thermal sensors to prevent overheating. Any help would be much appreciated. Thanks

On November 3, 2017 at 3:51am
Erteza Tawsif Efaz wrote:

i would like to know what to write in Reference as citation if i have wrote up a thesis by taking some information from this page, as an example i took *figure 1 charge stages of lithium ion* for my thesis but i couldnt find any citation for that picture. Need some help on citation for that.
have a great day.

On January 11, 2018 at 4:07pm
WrineX wrote:

Hi i wondered when you charge a battery with a charger can it ever read more then 4.20 volt on a multi meter ? the charger does use CC CV , but i want to see if there is an y difference when i feed the charger 4.3 volt (4 is minimum) or 6 volt which is still within the specs. i ask, this to decrease heat. i noticed giving the charger less voltage generates less heat and i wonder how low i can go. the charge current remains the same in all cases. i sort of want to force the charge chip a 4057A to manipulate as little as possible (less heat) but since it some how is longer on the charger i wondered if i am not over charging the bat

On January 14, 2018 at 9:33am
Shuu wrote:

I would like to know about quick charge (Qualcomm technology).
That make battey not stable right ?
Let’s explain about how quick charge effect to battery please !

On January 15, 2018 at 2:58pm
Ed V. wrote:

Hi, I have an Intergy Kodiak solar generator that uses a 1100 WH Li NMC battery.  They claim it has a 2000 cycle service life and they recommend leaving it fully charged, and on the charger at all times.  Based on your article, it seems to me I should limit charging to 40 - 50 % when I’m not using it and try to get by with a 70% charge to maximize the service life.  Is that correct?  I wonder why Intergy would recommend leaving it on a charger continuously.

On January 31, 2018 at 8:51am
michael porporo wrote:

do batteries need to be completely depleted before charging?

On February 8, 2018 at 12:59am
illumiin wrote:

I have a question! I’m using iPhone and i only charge my phone by Laptop via USB host. But when i check my phone by software such as “3utools” or similar…, i realize my phone (battery) has max voltage’s 4.47V when max capacity. I think it’s a Li-ion battery type, and at 4.2V, my battery only has 80% capacity! Is that normal???

On February 21, 2018 at 5:38am
DAHA wrote:

I have a question regarding how much the life time will be effected in an UPS battery which needs to maintain a “fully charged battery” for a long period of time(years). 
(With fully charged battery I thinking around 80% SoC)

1. Is it recommended to maintain battery voltage for 80% SoC for many years?
2. Is it better to lower SoC to 60-70%, will it prolong the total life time of the battery?
3. Is it important to do cell balancing even thou the SoC of battery is around 60-80% instead of 100%?

On March 2, 2018 at 5:19pm
Ken Maynard wrote:

I have a robot mower whose charging circuit has broken. It only deliver 1.5V instead of 24V. Normally the robot homes on 2 big spikes to get recharged. I just got a 6-cell stand-alone charger. I took the battery out and see that it has 6 terminals labelled
-, T,BH,Vcc,BS,+
If I connect the charger to + and - is is likely to charge, explode, or what? The manufacturer (Worx) doesn’t answer so I am in the dark here. I would be grateful for any info.

On March 12, 2018 at 4:39am
Kim wrote:

Does this applies to batteries that are not 4.2v at max charge?

On April 1, 2018 at 1:15pm
Wildeman Victor wrote:

What will happen with my Li Lion 18650 if i charge them only with cv and the current fluctates every secound, like charging on a Solar cell?
Lifetime crtitc? Capacity is a little less then cc cv…?

On May 7, 2018 at 11:26am
Scott Johnson wrote:

I’ve got a pair of 18650s I’ve been carrying as spares. They were fully charged about a year ago so they’ve been stable. I measured their voltage thinking I could learn something about their state of charge ... and they both measure 4.085 volts on a NIST-traceable calibrated voltmeter. Most of what I read here says that voltage is impossible and that it should be settled somewhere below 4V. Are they overcharged?

On May 8, 2018 at 10:41pm
Stephen Tice wrote:

I am using old 18650 cells from laptop computers hocked up in series to get 37.80 volts to run a 9 Led flush light. I works well and I have tested it several times. I discharged the battierys to -13%.The problem is I am charging the 9 cells up one at a time and it takes much time ! Is there a charger I can use that will charge at 37.8 plus volts that will do the same job with out damaging the cells?
2nd question, what % can I discharge this battery doun to without damaging the cells?

On July 13, 2018 at 9:43pm
Charles Sleep wrote:

I have a CPAP battery pack, a Medistrom, Pilot-12 Plus, cell type is described as “Industrial grade genuine rechargeable lithium ion cells manufactured by LG®” and I am recharging it with my semi truck’s invertor. Do I need a pure sine power supply?

On July 18, 2018 at 9:10am
Marcel wrote:

An e-bike battery (home made) with 12 cells in parallel is being charged to 4.10 volt end voltage
The cut off amperage is 0.1 amp and during the charging the current will slowly drop off from lets say 6A to 0.1A

During the charging the amperage will reach 0.5 Amp for example at which point the amperage per cell will be 0.5A/12 cells = 0.41mA possibly for an hour or longer

Will this damage the cells?
Is this considered trickle charging over a long period of time?

The solution would be a high power charger that can deliver 12 amps or more with a higher cut off amperage but my main concern is, will this damage the cells if the end voltage is set at 4.10 volt or possibly lower at 4.0 volt?

The issue here is not how to properly charge one cell but more what happens if you put multiple cells in parallel and the charge current per cell drops significantly which is mostly the case in high power applications such as e-bikes that require high amperage to run properly

On July 18, 2018 at 11:52am
Marcel wrote:

Stephen Tice wrote:

I am using old 18650 cells from laptop computers hocked up in series to get 37.80 volts to run a 9 Led flush light. I works well and I have tested it several times. I discharged the battierys to -13%.The problem is I am charging the 9 cells up one at a time and it takes much time ! Is there a charger I can use that will charge at 37.8 plus volts that will do the same job with out damaging the cells?
2nd question, what % can I discharge this battery doun to without damaging the cells?
I am using old 18650 cells from laptop computers hocked up in series to get 37.80 volts to run a 9 Led flush light. I works well and I have tested it several times. I discharged the battierys to -13%.The problem is I am charging the 9 cells up one at a time and it takes much time ! Is there a charger I can use that will charge at 37.8 plus volts that will do the same job with out damaging the cells?
2nd question, what % can I discharge this battery doun to without damaging the cells?

You could make two groups of 5 cells in series and 4 cells in series then connect the two groups in series and charge them separate with a (cheap) li-ion charger with balance charge capability

The cheapest charger I could find will only do 6s or 6 cells in series max.

You would have to do some research online and make groups with a balance connector (not that hard to do)

The lowest voltage for discharge is 3 volt per cell before you cause damage some cells can go to 2.5 volt but 3 volt is a safe cut off

There are cell voltage alarms available for RC hobby that can help out with a voltage alarm to let you know when the cells get to low

On July 18, 2018 at 12:01pm
Marcel wrote:

Scott Johnson wrote:

I’ve got a pair of 18650s I’ve been carrying as spares. They were fully charged about a year ago so they’ve been stable. I measured their voltage thinking I could learn something about their state of charge ... and they both measure 4.085 volts on a NIST-traceable calibrated voltmeter. Most of what I read here says that voltage is impossible and that it should be settled somewhere below 4V. Are they overcharged?

The voltage after charge will drop off or settle lower than the charge voltage, when charged to 4.2 volt the voltage will settle anywhere between 4 and 4.2 volt and over time it can drop lower due to to self discharge

At least that’s my experience with healthy li-ion cells

(they should hold 4+ volt over at least a couple of weeks)

On July 18, 2018 at 12:15pm
Marcel wrote:

Wildeman Victor wrote:

What will happen with my Li Lion 18650 if i charge them only with cv and the current fluctates every secound, like charging on a Solar cell?
Lifetime crtitc? Capacity is a little less then cc cv…?

cc or constant current is important because you don’t want to charge cells with a too high current, constant voltage is important because you don’t want to overcharge cells with too high of a voltage

so you can have a constant voltage of 4.2 volt with a start current of 30 amps, this will be bad for the cell

A proper charger will limit the current to lets say 1 amp and limit the voltage to 4.2 volt
The charger will drop the voltage down until the cell receives 1 amp, when the cell amperage drops below 1 amp the voltage goes up but will never go over the set 4.2 max. voltage

I Hope this helps

On July 18, 2018 at 1:43pm
Marcel wrote:

michael porporo wrote:

do batteries need to be completely depleted before charging?

No, li-ion batteries can be charged at any time, they don’t have to be empty

On July 18, 2018 at 2:01pm
Marcel wrote:

illumiin wrote:

I have a question! I’m using iPhone and i only charge my phone by Laptop via USB host. But when i check my phone by software such as “3utools” or similar…, i realize my phone (battery) has max voltage’s 4.47V when max capacity. I think it’s a Li-ion battery type, and at 4.2V, my battery only has 80% capacity! Is that normal???

When charging with usb and a cable that comes with your phone or is suitable for your phone your phone will charge until it reaches its maximum capacity
The electronics inside the phone and battery will prevent overcharging

Software may not be accurate when measuring voltages from the battery

When connected to computer usb or wall charger your phone will always charge until it’s full no matter what the maximum voltage of your battery is

On September 23, 2018 at 3:42am
David Maxfield wrote:

My Bosch EBike charger has failed and the replacement is quite expensive.Is it ok to just source an alternative cheaper brand of charger as long as the output voltage and current are the same ?

On September 26, 2018 at 1:34pm
Marcel wrote:

Q: David Maxfield wrote:

My Bosch EBike charger has failed and the replacement is quite expensive.Is it ok to just source an alternative cheaper brand of charger as long as the output voltage and current are the same ?

A: That should be ok because the electronics in the battery pack will balance the pack and cut off the charge current when the battery is full

Be aware that the original charger may have more than 2 connections (+ and -) that may have an effect on the charging process

To be 100% safe you should use the recommended charger

On October 9, 2018 at 5:47pm
neal wrote:

can this lithium battery be recharged?  label on battery says GEBC Lithium Battery, BATT-D103-4, REF:A340301 10.8V 19Ah, ASM by GE Battery, China 33/15

On November 5, 2018 at 1:32am
Tin Khaing Minn wrote:

Should I use PWM Solar Charge controller to charge Li-ion Battery. I think that Spike of PWM can cause fire or burn Li-ion Battery. Please confirm.

On November 14, 2018 at 2:39am
Fedrico wrote:

Hello, I have a LiFePo4 battery for an EV. I want to extend its life as much as possible. What would be the optimal charging time? (made of 2,5 Ah 3,3 V cells). Need to use 80% DOD.
Thank You!

On November 15, 2018 at 11:59pm
Terence Morris wrote:

I have two new 2600mAh camera batteries that I’m unable to charge properly after only a handful of charge cycles. The weird thing is when they are fully discharged the charger reports them as 90% charged. After charging to100% I only get around 5 minutes use from them whereas new they gave me around an hour (I use them to power a 7” camera monitor). I checked with a voltage meter and they definitely have zero voltage output when discharged. I doubt the charger is faulty as I have two identical chargers and both give 90% percentage readouts when the batteries are definitely flat. What is going on?

On November 26, 2018 at 4:00pm
Dwight Johnson wrote:


I own a 1919 Milburn Electric car and would like to purchase lithium LIFePO4 batteries instead of the using the original lead acid batteries.

The motor is a 76 volt 33amp DC GE motor from the era. The original system voltage was 84 volts (42 cells in 2 modules or 21 cells each)

The manual controller with 12 brass contact fingers is organized as follows :

“gear” 1 slowest speed, wheels beginning to turn, most ‘torque’
the motor is energized at 42 volts with the 2 modules in parallel and a resistor in place

“Gear” 2 slightly faster and ‘torque’ still required to gain speed
The motor is energized at 42 volts with the 2 modules in parallel and less resistance

“Gear” 3 medium speed
The motor is energized at 84 voltswith the 2 modules in series and even less resistance

“Gear” 4 high speed least amount of ‘torque’
The motor is energized at 84 volts with the 2 modules in series and no resistors

In “off” mode the lead acid cells were placed in series and the charger provided 84 volts.

I have been talking to a lithium cell supplier who is willing to supply sufficient LIFePO4 120amp cells in 2 seperate and equal modules to provide nominally 42 volts each and a BMS for each

These modules are recommended to be wired in series only for 84 volts and that they stay that way

He does not recommend that they be connected alternately in parallel for 42 volts 240 amps.

I am assuming that there is a concern that the 2 lithium ion modules will become out of balance with each other and risk fire and explosion

A consistent 84 volt system will not work in this car

Any suggestions that would lead to successful usage of lithium cells in 2 equal but separate 42 volt modules?

Thank you

On December 4, 2018 at 11:42pm
Rafael wrote:

I would like to know, how do I develop a security charger that cuts off power at the time the phone is in use.

On January 8, 2019 at 12:05am
pablo reyes wrote:

Can I charge my 72V li batteries with 60v charger?