BU-303: Confusion with Voltages

Explore why some battery packs pose odd voltages and how this affects the user.

A battery is an electrochemical device that produces a voltage potential when placing metals of different affinities into an acid solution (electrolyte). The open circuit voltage (OCV) that develops as part of an electrochemical reaction varies with the metals and electrolyte used.

Applying a charge or discharge places the battery into the closed circuit voltage (CCV) condition. Charging raises the voltage and discharging lowers it, simulating a rubber band effect. The voltage behavior under a load and charge is governed by the current flow and the internal battery resistance. A low resistance produces low fluctuation under load or charge; a high resistance causes the voltage to swing excessively. Charging and discharging agitates the battery; full voltage stabilization takes up to 24 hours. Temperature also plays a role; a cold temperature lowers the voltage and heat raises it.

Manufacturers rate a battery by assigning a nominal voltage, and with a few exceptions, these voltages follow an agreed convention. Here are the nominal voltages of the most common batteries in brief.

Lead Acid

The nominal voltage of lead acid is 2 volts per cell, however when measuring the open circuit voltage, the OCV of a charged and rested battery should be 2.1V/cell. Keeping lead acid much below 2.1V/cell will cause the buildup of sulfation. While on float charge, lead acid measures about 2.25V/cell, higher during normal charge.


In consumer applications, NiCd and NiMH are rated at 1.20V/cell; industrial, aviation and military batteries adhere to the original 1.25V. There is no difference between the 1.20V and 1.25V cell; the marking is simply preference.


The nominal voltage of lithium-ion is 3.60V/cell. Some cell manufacturers mark their Li-ion as 3.70V/cell or higher. This offers a marketing advantage because the higher voltage boosts the watt-hours on paper (voltage multiplied by current equals watts). The 3.70V/cell rating also creates unfamiliar references of 11.1V and 14.8V when connecting three and four cells in series rather than the more familiar 10.80V and 14.40V respectively. Equipment manufacturers adhere to the nominal cell voltage of 3.60V for most Li-ion systems as a power source.

How did this higher voltage creep in? The nominal voltage is a function of anode and cathode materials, as well as impedance. Voltage calculations include measuring the mid-way point from a full-charge of 4.20V/cell to the 3.0V/cell cutoff with a 0.5C load. For Li-cobalt the mid-way point is about 3.60V. The same scan done on Li-manganese with a lower internal resistance gives an average voltage of about 3.70V. It should be noted that the higher voltage is often set arbitrarily and does not affect the operation of portable devices or the setting of the chargers. But there are exceptions.

Some Li-ion batteries with LCO architecture feature a surface coating and electrolyte additives that increase the nominal cell voltage and permit higher charge voltages. To get the full capacity, the charge cut-off voltage for these batteries must be set accordingly. Figure 1 shows typical voltage settings.

Nominal cell voltage Typical end-of-discharge Max charge voltage Notes
3.6V 2.8–3.0V 4.2V Classic nominal voltage of cobalt-based Li-ion battery
3.7V 2.8–3.0V 4.2V Marketing advantage. Achieved by low internal resistance
3.8V 2.8–3.0V 4.35V Surface coating and electrolyte additives. Charger must have correct full-charge voltage for added capacity
3.85V 2.8–3.0V 4.4V Surface coating and electrolyte additives. Charger must have correct full-charge voltage for added capacity

Figure 1: Voltages of cobalt-based Li-ion batteries. End-of-charge voltage must be set correctly to achieve the capacity gain.

Battery users want to know if Li-ion cells with higher charge voltages compromise longevity and safety. There is limited information available but what is known is that, yes, these batteries have a shorter cycle life than a regular Li-ion; the calendar life can also be less. Since these batteries are mostly used in consumer products, the longevity can be harmonized with obsolescence, making a shorter battery life acceptable. The benefit is longer a runtime because of the gained Wh (Ah x V). All cells must meet regulatory standards and are safe.

The phosphate-based lithium-ion has a nominal cell voltage of 3.20V and 3.30V; lithium-titanate is 2.40V. This voltage difference makes these chemistries incompatible with regular Li-ion in terms of cell count and charging algorithm.

Last Updated 2017-05-09

*** Please Read Regarding Comments ***

Comments are intended for "commenting," an open discussion amongst site visitors. Battery University monitors the comments and understands the importance of expressing perspectives and opinions in a shared forum. However, all communication must be done with the use of appropriate language and the avoidance of spam and discrimination.

If you have a suggestion or would like to report an error, please use the "contact us" form or email us at: BatteryU@cadex.com.  We like to hear from you but we cannot answer all inquiries. We recommend posting your question in the comment sections for the Battery University Group (BUG) to share.

Or Jump To A Different Article

Basics You Should Know
The Battery and You
Batteries as Power Source


On March 3, 2011 at 5:06pm
BWMichael wrote:

its funny how people think a lithium battery with 3.7v written on the packaging is better than one that says 3.6v

On March 7, 2011 at 7:03am
Edward Baxter wrote:

I am in Mexico. Can I use a 3.6v lithium as a replacement for a 3v lithium in my dive computer.

On March 18, 2011 at 3:05am
MAHESH wrote:

want details of batteries

On May 14, 2011 at 5:34am
dean mancis wrote:

hi just wondering what is the current flow in a singel 12v headlamp circuit with 100w globe is it 10A?  And how much current will flow through a cicuit that has a 12volt power supply and a resistance of 6 ohms is it 2 Amps .  What is required to drive 1.5A of current through a 30 ohm load is it 45v?

On May 25, 2011 at 5:56am
Robert Atkinson, Jr. wrote:

The author made a slight error in the formula for energy. Volts (V) times Amps (A) equals Power in Watts (W), not energy (Wh). Since power is energy per unit of time, then Power (W) x time (hours) equals energy (Wh). To convert Watt-hours to Joules (the MKS measurement system’s preferred unit) Multiply Watt-hours by 3600 sec/hour to get Joules (1W= 1Joule/sec, and 3600 sec=1 hour, or 60 sec/minute x 60 minutes/hour= 3600 sec/hour).

On August 25, 2011 at 12:19pm
Ian wrote:

What voltage is required to charge a 12 volt gel battery . IAN

On December 3, 2011 at 9:09pm
Man Man wrote:

“Italso” - sounds like an Italian battery company. Needs a space, as does “series.Let”.

On December 3, 2011 at 9:10pm
Man Man wrote:

And “(OCV)attained”.

On September 19, 2012 at 2:23am
mark wik wrote:

love your site. hopefully i will learn many things and impress my friennds and associates with my knowledge of battery and charging technology. thanks, mrw

On January 22, 2013 at 3:13am
shaibu wrote:

how to calculate the total heat loss of VRLA batteries.

On August 26, 2013 at 7:22am
omar wrote:

Can i charge my li-ion battery with a 9v ac adapter?

On November 26, 2013 at 3:29am
Ajay Pundir wrote:

just love your site. it has increased my knowledge of batteries and charging technology. thanks

On January 20, 2014 at 4:42am
jeeva wrote:

Sent me email for battery information

On February 27, 2014 at 4:04am
harry potter wrote:

do you use skype? If yes we can also discuss there. -  It would be awsome if a discussion of e.g. batteries could be done between different scientist via skype or something else, so that everyone get soon help…
i just want to ask something about that battery and explain me how to make it in russia\
harry potter movies in order

On April 20, 2014 at 9:52am
ruby wrote:

I wonder how many more projects are out there secretly

On October 6, 2014 at 7:01am
sandeep wrote:

Sir is there any problem in charging a 1.2 volt battery by a 9 volt dc. 2000 mA output charger

On December 2, 2014 at 1:57am
Zeinab wrote:

hello people , actually i am inquiring about OCV most problem and how it affects the battery

On December 3, 2014 at 3:51am
SHAILENDRA jain wrote:

can we connect in a battery bank of 12 v 150ah battery with 12 v 100ah battery .

On January 6, 2015 at 6:40am

My car is alto k10 maruthi, pls inform me using horn details,battery volts and horn volts.

On February 7, 2015 at 9:54pm
Iain wrote:

I removed a 3 volt CR2 lithium battery from my security system because I had a low battery reading. I am puzzled because after removing it, I found that the battery still read 3 volts. Can you explain this?

On February 17, 2015 at 12:47am
Tevita Kirailevu wrote:

When reading an analogue meter , which place in it should i read the battery voltage (can you send a image of it on where to locate it.

On February 18, 2015 at 10:03am
tony wrote:

i am not satishfy with the seriese combination of cells.

On March 18, 2015 at 3:59pm
James Traxel wrote:

My instrument rechargeable battery got weak and I went to replace it.  It is an “A” size battery.  When I measured the voltage it was 1.8 v.  How can this be?  The battery that I purchased was NiMH of 1.2 v so I’m left scratching my head.

On March 22, 2015 at 6:46pm
JM wrote:

If you still have the curiosity itch, try measuring the battery voltage under load (while it’s being used by a device). This should give you an accurate reading as to how much voltage your battery is really pushing. Do this at your own risk and be careful. Plan how you’re going to go about measuring it (don’t allow the positive and negative to touch each other and you’ll be fine). Probably not worth the risk, but the idea is there if you want to try it.

On March 24, 2015 at 1:16am
krishna wrote:

How much highest ratting of dc batteries

On April 22, 2015 at 9:16am
Tom wrote:

I am currently charging a battery (inside a device, and I have no details about it, I just know it is rechargeable).
Using my universal power supply, I have the voltage up and the current reduced to 200mA. Currently the voltage is at 8.87V. any ideas what voltage will indicate a full charge?

On August 31, 2015 at 6:36pm
Bishwo wrote:


I have a 6V battery to run my system which also works in 6 volt that draws 0.5 AH. I made a parallel combination with two 12AH to make 24 AH so that I don’t need to recharge the battery for 48 hours. Once accidentally connected negative to positive and positive to negative which damaged the system and I had to repair it. DO you think that accident has any impact on the battery? Can I use the same battery again to run the system?

On September 24, 2015 at 11:35pm
HardwareFreak wrote:


How to calculate the time taken for a Li-ion battery to discharge from 4.2V to 3.4V, @ 2A load current…?
Can anyone pl help.

On October 2, 2015 at 7:54am
enver salimov wrote:

i thing this is so beatufull

On November 5, 2015 at 8:52am
JEC wrote:

Typical battery charger puts in Amps not volts correct?
As dc amps goes in, doesn’t battery voltage increase?

On January 28, 2016 at 11:28pm
NightShadow wrote:

So I have something that needs 150 volts to be powered. stun guns on average carry a punch of about 1.5 million volts. how is it that I can’t find a battery that gives me an output of 150 volts? what battery should I use and how long will it last if it would be running for 8-10 hours a day?

On May 5, 2016 at 1:42pm
Alan Smith wrote:

A table showing the chemistry and the voltage would give far greater clarity than this style of writing, the information *is* good but not easy to pick out the most relevant facts.

On July 1, 2016 at 4:46am
gat wrote:

why complicate using 9v battery

On July 23, 2016 at 1:43pm
framistat wrote:

Looking at a Sanyo Eneloop bicycle circa 2010, battery packs no longer available even from Japan (Amazon or Rakuten).  The bike has a 250W brushless motor.  The battery pack is stated as 25.2V 5.7Ah.  Most 250W motors today are 24V.  So I’m wondering why they would have used a nonstandard lithium ion 25.2V battery pack… must be 7 cells?

On August 10, 2016 at 10:54pm
Anish bhurke wrote:

What is the expected open circuit voltage of a 12V lead acid battery

On September 17, 2016 at 10:56pm
Zain Tariq wrote:

We recently Installed lead Acid Battery Make Happecke Model: 11GroE 1100
2V, 1100Ahr,Cn/1210Ahr C10 Ufloat = 2.23V/cell, total Voltage 125V,
After one month we loosed the AC supply and we used this battery bank but after 4hours battery voltage reached on 70V and now these all cell voltage not going to up. please advise to us how we can solve this problem.

On November 25, 2016 at 2:36am
Gabo wrote:

But nowadays we have Li Ion batteries in our mobiles with voltage over 5 volts ... how is this possible?

On January 31, 2017 at 9:42am
Gowda wrote:

what will be the cell voltage if battery reaches its 80% degradation

On January 31, 2017 at 12:43pm
Alan Smith wrote:

without doing a proper discharge graph - the only real way to work it out - how about

V = F - [( F - L)  * D]

V = approximate Voltage
Fully Charged Voltage - F
Voltage of Discharged cell - L
Degradation - D ( so 80% is 0.8 )

On May 15, 2017 at 4:13am
Harsh Jain wrote:

Excellent information