BU-808a: How to Awaken Sleeping Li-ion

Learn what you can do to prevent a Li-ion battery to fall asleep.

Li-ion batteries contain a protection circuit that shields the battery against abuse. This important safeguard also turns the battery off and makes it unusable if over-discharged. Slipping into sleep mode can happen when storing a Li-ion pack in a discharged state for any length of time as self-discharge will gradually deplete the remaining charge. Depending on manufacturer, the protection circuit of a Li-ion cuts off between 2. 2V and 2.9V/cell. (See BU-802b: Elevated Self-discharge)

Some battery chargers and analyzers (including Cadex), feature a wake-up feature or “boost” to reactivate and recharge batteries that have fallen asleep. Without this provision, a charger renders these batteries unserviceable and the packs would be discarded. Boost applies a small charge current to activate the protection circuit and if a correct cell voltage can be reached, the charger starts a normal charge. Figure 1 illustrates the “boost” function graphically.

Sleep mode of a lithium-ion battery

Figure 1: Sleep mode of a lithium-ion battery

Some over-discharged batteries can be “boosted” to life again. Discard pack if the voltage does not rise to a normal level within a minute while on boost.

Do not boost lithium-based batteries back to life that have dwelled below 1.5V/cell for a week or longer. Copper shunts may have formed inside the cells that can lead to a partial or total electrical short. When recharging, such a cell might become unstable, causing excessive heat or showing other anomalies. The Cadex “boost” function halts the charge if the voltage does not rise normally. 

When boosting a battery, assure correct polarity. Advanced chargers and battery analyzers will not service a battery if placed in reverse polarity. A sleeping Li-ion does not reveal the voltage and boosting must be done with awareness. Li-ion is more delicate than other systems and a voltage applied in reverse can cause irreversible damage. 

Storing lithium-ion batteries presents some uncertainty. On one end, manufacturers recommend keeping them at a state-of-charge of 40–50 percent, and on the other end there is the worry of losing them due to over-discharge. (See BU-702: How to Store Batteries) There is ample bandwidth between these criteria and if in doubt, keep the battery at a higher charge in a cool place.

Cadex examined 294 mobile phones batteries that were returned under warranty. The Cadex analyzer restored 91 percent to a capacity of 80 percent and higher; 30 percent were inactive and needed a boost, and 9 percent were non-serviceable. All restored packs when returned to service and performed flawlessly. This study shows the large number of mobile phone batteries that fail due to over-discharging and can be salvaged.

Last updated 2016-01-20

*** 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 question, require further information, have a suggestion or would like to report an error, use the "contact us" form or email us at: BatteryU@cadex.com. While we make all efforts to answer your questions accurately, we cannot guarantee results. Neither can we take responsibility for any damages or injuries that may result as a consequence of the information provided. Please accept our advice as a free public support rather than an engineering or professional service.

Or Jump To A Different Article

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


On April 19, 2011 at 1:25pm
fhhuber wrote:

Note that some low voltage cutoffs are programmed for a SET voltage, others are based on RELATIVE voltage.

A set voltage cut-off would turn off power at the same voltage regardless of charge state when the battery was plugged in.

A relative voltage cut-off “detects” the battery voltage at plug-in and then the cut-off is a percentage of that voltage.

Because many hobbyist Radio Control system ESCs (Electronic Speed Controllers) use the RELATIVE voltage, it is imperative that a battery used in these applications be FULLY charged when it is plugged in.  A partially charged battery being plugged in can result in the cutoff being low enough to damage the battery.

On February 14, 2012 at 12:47pm
tytower wrote:

I had such a battery Hit it with a 40V pulse for 500 nsecs and it came good immediately

On April 3, 2012 at 7:59am
guy00 wrote:

I’ve tried to charge a battery that was not used for a year, but when i stopped using it it had a partial charge… now i measured it with a multimeter and it showed 0v (the protection kicked in). But when measuring between the negative and positive terminal AND the middle terminal (cell phone battery), it showed 1.09 and 1.04, respectively. I thought the battery is @ 2.13v, and tried to recharge it directly from the cell phone charger (red wire to the positive and black to the negative). A spark flied, but i continued to charge for another minute. Then i took a multimeter, measured, and it showed 3.2v smile. Then i continued to apply charging for another 2mins and got the battery up to 3.48v. Currently left the battery like that, it lits up a white LED very bright. I’m wondering is that battery safe for using now, i dont really need that battery, but if its working fine maybe i’ll find use for it since the cell phone i got it from is dead smile

On April 22, 2012 at 3:36am
Brian wrote:

Too involved and way off the topic.  How do I prolong lithiom ion battery life? :/

On June 25, 2012 at 10:44am
jake wrote:

What no one has said here is that Lion Batteries are prone to explode…Just see youtube.

Be very careful while resurrecting batteries always work under a perspex sheet with gloves., You can do almost any batteries..

On July 16, 2012 at 10:11pm
krist0ph3r wrote:

can i boost a cellphone battery using the regular charger, or do i need some special equipment to do so? would 5V/1A be enough?

On December 13, 2012 at 11:47am
Mad Monty wrote:

If Li ion batteries become unpredictably dangerous if left discharged too long, it would seem that no “found” batteries (e.g., old laptop unused for a “long time”) would be safe to use.  Have I got that right?  And following up, how best to dispose of them?

On January 11, 2013 at 2:37am
fred hreyer wrote:

How do you estimate when a lithium battery is at 40%?

On January 29, 2013 at 1:10pm
AbdEl-Rahman wrote:

That’s actually very great what you guys are writing , but actually needs some simplification on what should be done to boost it again on duty ,ya know.
So my request is for you guys to offer me a solution (SAFE Of course) to do to my iPhone Li-ion polymer battery ,that also doesn’t include removing it out of the phone .
I would be very grateful to have an expert opinion ,because I am done with those videos that never give a solution straight to a person,ya know .
Thank you for your time all

On April 5, 2013 at 11:32am
sam wrote:

guys can you please help me to restore my fully discharge li ion battery on my laptop,its about 5 months later after i bought it,i frequently using ac connection so the battery i’ve only used it ones a week,,but now its already fully discharge and i don’t how to awaken it..i already put it on my laptop but it;s not charging anymore,,,


On April 13, 2013 at 2:26am
Oscar Ormond wrote:

Take a technology that is very very difficult to get right then after spending hundreds of millions of dollars on research and it still not very good, knowing people want to use it simply go ahead and put it on the market. Take the money and run. Simple explenation.

On April 13, 2013 at 2:10pm
Mad Monty wrote:

So you want simple instructions on bringing a Li-ion back to life?  Here it is:  Choose either (1) to buy an expensive smart charger (like Cadex, above - no , I don’t have any stake in the company); or (2) Replace the battery.  That’s it.

Only those who can tolerate a brief explanation should read further. 

The reason not to try to fool with it yourself is that it really can go up in your face.  Literally.  Lithium-ion chemistry is not only more dangerous but also more complicated than NiH.  All the stuff you don’t want to read or try to understand is exactly the stuff in need to do to prevent a serious accident.  A smart charger figures it all out for you so you don’t get burned or blinded or destroy your laptop or whatever.  If you try to do it yourself, you have to think through all the algorithms, make complicated measurements, and administer the charge, all the while continuing to monitor and measure and make adjustments until either the battery reaches its maximum charge or you determine it is beyond hope.  (Ever look inside a laptop battery?  There is a whole slew of sensors and circuitry attached to each cell, whose primary requirement is to prevent harm and lawsuits.)

Yes, some people – many people – have been lucky when they have tried to rejuvenate batteries in simple ways.  If they played Russian roulette, five out of six would think that was pretty safe too.

Madly yours,

Mad Monty

On May 4, 2013 at 5:21pm
Parker Thornton wrote:

Any Batteries Plus or Batteries Plus Bulbs can recycle them for you. Please don’t throw them away.
They also have a Cadex and a laptop battery reconditioner and can restore batteries for you if you ask, usually for free

On May 21, 2013 at 2:57am
carribawhore wrote:

If you have an old camera li ion cell charger, like canon. You can easily bring dead batteries back to live. Without danger. Just connect the + and ~ of the charger with wires directly on the poles of the li ion akku. Then insert an empty camera battery in the charger and there you go.

On June 20, 2013 at 2:47pm
Mike wrote:

to AbdEl-Rahman: unfortunately you would have to take to battery out of your iphone, you need to jump start the li-ion battery with a high voltage at a low amperage which in turn would fry the circuits on you phone, there are tons of walkthroughs on how to remove and replace iphone batteries online, its not that difficult especially if you document where each screw goes and how you took it apart piece by piece.

MAC/Windows professional with 10+ years tech experience

On June 28, 2013 at 12:36pm
Sean M wrote:

“How do you estimate when a lithium battery is at 40%?”

As a rough example, if your battery pack normally lasts, say 10 hours under continuous use, you’ll reach 40% of usable capacity after six hours.

If all you go on is variables, you won’t know.  the simplest is to use the above method.

On July 10, 2013 at 2:52am
s.pirie wrote:

my wife has been using e cigarettes for three months now using ego t brand who give no back up for faults , these use lithium ion batteries , the fault is no operation of the atomiser although the battery voltage shows around 3.8 which is what is expected although the 3.8v is showing at the battery without pressing the operating button which you would expect this to make the atomiser work constantly with no need to press the button, this does not happen . Does anyone have any idea how i can fix this fault ? My wife is in desperation as all of her 5 batteries faulted on the same day which is very curious .

On July 20, 2013 at 2:52am
emmit wrote:

The batteries you have for the e-cig have a turn on / off sequence 5 pushes in 3 seconds or less will turn the device on (push on/ push off non latched)...and the same will turn the battery off..the battery also has a fail safe It will auto shut off if the button is depressed for more than 10 seconds (could be 7/8/9 seconds depends on battery type eg.ego

On September 24, 2013 at 12:26am
Yu Jun Gu wrote:

Just brought two efest 14500 protected batteries back to life. Thank you for this article!! They must have been in storage for a very long time, got them from a friend who didn’t want them anymore. Was having a helluva time. Charger didn’t register them. The way I woke them up was sticking them into a AA battery box I had laying around and connecting an 18650 (Positive to positive negative to negative) to the lead wires for 30 seconds or less. Freaked me out the first time around because the 14500 got real hot and I thought I had thermal runaway on my hands. But it cooled off again and when I checked the voltage it was at 3.07v. Repeated that step with the second battery just much shorter duration of charge with the 18650 this time around, like 10-15 seconds. Woke it right up. In the charger now recognized and charging as usual.

On September 25, 2013 at 3:18pm
mark wrote:

Does anyone have a working battery for a schwinn Transit bicycle i can buy?

On November 6, 2013 at 7:24am
Rodelion wrote:

Often I get frozen cells (showing 0V) to work again by putting it in a universal li-ion charger several times. Universal li-ion chargers give all kinds of pulses to the cell to figure out what kind of voltage and polarity the cell has. I think those pulses make the battery work again.

On another instance, with a Nikon EN-EL5, this didn’t work…
After a lot of effort I found out there are two hidden contacts underneath a little seal, so five in total. Through trial-and-error I found out that the hidden contact next to the ‘+’ corresponds with the positive terminal, and the one next to the ground, corresponds with the negative terminal. I think there’s a condenser between these two contacts, and I used a 6V lithium battery to charge it. When I got at about 3.7V, the battery suddenly started working again.
While doing this, both batteries became warm, but not quite hot. If a cell becomes really hot, I think you’re on dangerous ground.

On November 23, 2013 at 10:08pm
David wrote:

I have a weird issue with a protected 14500 battery. The battery shows 3.4v and will lit up a small LED (not a Cree or high output LED), but will not take input charge by the charger (charger light green like if it was not charging instead of orange) and when trying to boost it up using another 4.2v 14500 battery connecting + and - together, like mentioned above, it doesn’t seem to work at all, i.e. the defective 14500 won’t accept any input. It has about 200ma left out of ~600mh max capacity and will not power up my Cree P4 LED flashlight at all while the other 14500 battery will (even a 1.2NiMh battery doesn’t have problem powering this light).

Now I’m thinking the protection circuit might be defective and locked itself up whenever I try to input voltage/current or draw too much current out of it. Would there be anyway to save this battery by either resetting/bypassing the protection or simply physically removing the protection PCB ? It’s a brand new battery fresh from the store, and although they’re sending me a replacement one anyway, I’d hate to waste a salvageable product.

Thanks !

On December 17, 2013 at 7:31am
RKSINGH wrote:


On December 29, 2013 at 4:18pm
johny wrote:

according to what i’ve read, you can revive a dead li-ion with a low-current trickle charger. if the battery does not spring past 2.5 volts within one minute of trickle-charging, then the battery should be discarded. even if keeping on the trickle longer than one minute revives it!

is because the battery chemistry changes after it’s discharged and unused too long, making it dangerous to revive or use.

if it takes longer than one minute to revive, then the battery is dangerous, and should be discarded.

how to revive:

i don’t understand what this guy is doing:

On January 24, 2014 at 10:09am
jach wrote:

read again what mad monty wrote above. wise words. lithium chemistry is POTENT, experimenting with advice provided in a forum without understanding the basics of what your dealing with isnt recommended.and is literally russian roulette ,attempting to duplicate what worked in someone elses case , may explode in your face

On February 6, 2014 at 4:34pm
Sailor Jo wrote:

Very enlightening article. Still, I need to do some more research in order to understand the intricacies between the various types of lithium batteries.
The reading made me aware of the charger PIXO C4. I thought I found the ultimate charger until I checked the German manufacturers web site and the batteries that cannot be charged with this unit. A real eye opener, especially as it cannot charge the 18650 batteries that I have a problem with. Just too bad.

On March 4, 2014 at 9:43am
Emil wrote:

I just waked to life two 18650 batteries that came from a dead laptop battery I opened, the battery had 8 cells, four was complete dead, two was good and two had around 2V.
I used a iMax B6 charger and used NiMH charging with 0.1A current limit, charged the battery untill it shown 3.2V and then swopped over to lithium charging.
I put a iron pot over the battery lying on my concrete floor in the garage while I charged, in case the battery was blowing up or starting to burn.

On March 28, 2014 at 12:32am
e2cc_guru wrote:

I have designed a system which uses a 7.4 V, 6,6AH Li-Ion battery pack (18650) in the configuration 2S-3P. It is charged using a uC based software algorithm which is CC till 8.4V and then CV till current falls below 0.05C. I charge the battery using a 12V DC charger or a 12 V Solar Panel. Obviously there is a bick-converter in between which manages the voltage applied to the battery.

Recently I am getting field complaints that batteries which go to sleep would not revive using the software charger.

Can any one suggest what is wrong or what I should try? Please ask if you need more information.

On September 1, 2014 at 11:37pm
Paolo wrote:

Can I try to awaken a li-po battery from a Thinkpad notebook?
The Thinkpad don’t charge it.

On September 9, 2014 at 8:41am
usmc_0143 wrote:

I just got my Defeat 2500mAh IMR 18650 3.7V LI-MN batteries in the mail on Saturday (and today is Tuesday). I charged the batteries on Sunday and got my vapeing mod on Monday. I went to put the battery in and shortly after “trying” to Vale the battery got hot. I took it out and it looks like on the bottom of the battery the purple skin either peeled or got burned. I waited awhile for to cool off and the charger doesn’t even recognize there is a battery there. Any ideas what happened and if I can do something to get the battery working again?

On September 10, 2014 at 2:40am
emmit wrote:

Hi what EC mod have you tried to vape using this battery/ Most vaping mods have built in battery protection..
Is this the corrent battery for that mod? is it flat top,nipple top? some mods only accept non protcted batterise, and some with battery protection will accept protected batteris

I have many modss i mainly use a vamo with 3.7v non protected flay top

Art smile

On September 10, 2014 at 7:13am
usmc_0143 wrote:

I have a Stingray X MOD. I don’t know if only accepts protected or non proctected, but the two batteries that I do have are I believe non-Protected. It is a flat top. How do you know if the mechanical mod has a built in battery protector, and whether or not it only accepts protected or non-protected?

On September 10, 2014 at 7:56am
emmit wrote:


Stingray X Style Stainless Steel + Copper Mechanical Mod 18350 / 18500 / 18650
  510 threading connection
  Copper body wrapped with stainless steel
  Copper top cap wrapped with stainless steel with floating pin and vent holes
Is this the mod you have? 

Bottom magnetic firing button, the locking ring is NOT reverse-threaded
  Locking ring material: Polished stainless steel
  Silver plated copper battery contacts
  Comes with a hybrid adapter and a 510 drip tip
  Houses single 18650/18500/18350 battery (batteries sold separately)
  22mm external diameter
  18.6mm internal diameter

Connection Threading 510
Telescoping Mod No
Variable Voltage (VV)  No
Variable Wattage (VW)  No

Defeat 2500mAh IMR 18650 3.7V LI-MN

cant find this battery on web search

can I take it that you are from the USA?

where did you get that battery from? was it fast tech same as the stingray X

sounds like a short to me,Glad it didnt happen in your pocket!!! ...very painful

what atomizer are you using? have you checked for shorts on that and what

ohms/resistance on atty



On September 10, 2014 at 8:05am
Usmc_0143 wrote:

That is the exact mod that I have except mine is black but same one. No I haven’t checked for shorts. I friend at work is my expert. He is the one I go to for questions and to build my coils and stuff. I really new to the mechanical mod universe. I got the battery from Amazon. It’s Effest brand.  My atomizer is TOBH V3 Atty.  I got my mod from fluid apes.com as well as the atomizer.

On September 10, 2014 at 9:27am
emmit wrote:


have it checked for shorts on mod ans atty if okay try this type of battery as a test 18650 3.7V UltraFire4500mAh PCB Protected Li-ion Rechargeable Battery $5.00 on fleebay.com cheap as chips..the effest is the rolls royce of battery but not for your mod….you need protected batteries..you have proll fried the effest analso you can get an all in battery and mod protector using a Authentic Sigelei Variable Wattage Kick Module for Mechanical Mod from your supplier for about $10.00

once you have it sorted buy effest or sony protected batts


On September 29, 2014 at 8:12pm
Li wrote:

I have a Hitachi drill with 10.5V battery (BLC1015).  after 3 years of not using, the battery does not charge any more.  checking the voltage reveals that it has only 2.6V left.  I took a USB charger (an old LG cell phone charger 0.2A, 5V) and cut the end and exposed the wires.  stripped the end, and connected with the battery red to +, yellow to - with two metal paper clips.  there is not much change after 15 minutes, so I let it go over night.  the voltage became 3.1V.  I placed the battery to its original charger, and bingo! it started to charge.  the battery works now with the drill.  Interestingly, the spare battery would cost 50 dollars, but buying a new drill with two batteries and the charger would cost 90.  I got the idea from here and a youtube video, and figured that it could be useful to some folks who would get to this site.  it saved me fifty dollars and reduced waste.  I think the key is the slow charging of the battery to over the limit set by the charger.

On September 29, 2014 at 9:39pm
sahafdeen wrote:

my li-ion mobile battery 2500mah , working well upto 50% ,after sudden drain and directly come to 11%,,  only 3 months completed (buying), anyone give solution????

On November 19, 2014 at 1:37am
Stan wrote:

I had suffered the same “battery dead, not charging after complete discharge” scenario some two weeks ago on a brand new hp06 battery that had barely lasted a month. The older one “died” in the same way, although it was well within its final leg after a couple of years of usage and it barely lasted half an hour on idle! I took it apart for curiosity and some newbie studies. Anyway, the replacement would not charge at all so I decided to try reviving it from its deep sleep. I used an ordinary multi-voltage AC-DC adapter and applied 12v and 1A for a second and voila! The battery is now charging in the laptop. The current capacity is steadily rising by the minute and the temperature is normal. I’m keeping an eye out for any abnormal rise in temperature, but so far nothing alarming. I plan to recalibrate it after this charge cycle and will definitely post on any success or failure. If this works, I will be saved lots of money replacing the battery and the inconvenience of returning it to the dealer in pursuit of warranty facilitation.

On November 19, 2014 at 7:59am
Stan wrote:

More good news! The battery charged to full capacity as it normally would, without any unusual occurrences. As I type this comment, it still has 8% charge as it has been gradually discharging for the past three and a half hours on light usage (non-stop music playback, screen set to not dim or turn off and minimal work on some worksheets. The music is playing back from an external hard drive without an external power source). I know that it could have lasted even longer with the laptop sitting idle, but I wasn’t so patient to wait for a slow discharge. I’m never gonna discharge it completely again, but I want it to get critically low (3%) and let it shut down then charge it full capacity while the laptop is off. I must say I’m happy with the results, it’s like nothing ever happened to the battery despite having stayed “dead” for at least three weeks. I was mostly concerned about permanent damage to the cells due to staying in that state for too long, but my fears are no more! Thanks battery university for this priceless piece of information, saved me bucks for a smart charger or God knows what else I was gonna spend on to get out of this situation!

On January 11, 2015 at 3:18am
nihal wrote:

i have a ipod . with the same kind of battery.but i lost it and got it after many days.so the battery is completely drained.now how to fix it.do anyone have a solution other than changing the battery

On February 16, 2015 at 12:43am
prince ashiru wrote:

please my aspire one laptop battery was run down and i try to charge it in the 3rd day but its doesnt charge and the battery is last for upto 4 hours before ...
now its said plugged in, not charging…
please what can i do to get the battery on back

On April 14, 2015 at 12:31pm
Rick Whitehouse wrote:

Dear Battery University:
  I have a Ravpower 5600 mAH external battery, and charger for recharging my cell phone. The unit comes with a handy flashlight; unfortunately after placing the unit in my lunch bag, I think the flash light accidentally came on. After a few days I took out my Ravpower 5600 to charge my cell phone. I found my poor little charger completely dead. Is there a safe procedure for recovering my cell phone charger now? If I figure out what to do before getting my answer, I’ll be sure to share the info with Battery University.
Best Wishes,

On June 21, 2015 at 7:56pm
Clague wrote:

Left my phone in car in direct sunlight. It was over 100F in car. Phone shut off and was burning hot. Battery was performing poorly needing daily recharges even with little use. To cool phone down I stuck it in freezer and forgot about it. About three hours later I took it out. After thawing for about an hour I tried turning it on and was surprised that it started up and the battery was 85%. It has been over a day now and battery is still at 57 percent without having been charged.

On September 11, 2015 at 9:04am
Gaser wrote:


  My son HP Touchpad was left till it is drained. Left it in the charger for more than a week with no hope. I decided to crack it open and get the battery out to check if the battery or the circuit has an issue.

  At the first, the battery didn’t read any volt. The battery has 5 connectors 2 Red, 2 Black, 1 Green, 1 yellow, and 1 blue

Tried to charge it on Red & Black terminal using my Smart Charger, but since the charger couldn’t read the volt it reported over voltage error.

So decided to remove the rapping and see the battery, so I found that the battery has a circuit inside it, and the actual battery has 3.4 volt. So remove/desolder the battery from the circuit and charged it using my charger, and not it is 4.18v, but when connected to its circuit still doesn’t read anything.

I purchased another replacement and has the same issue with it, so not sure if there is something is needed to be done to activate the circuit, or am I done and should get my son another tablet.


On November 29, 2015 at 9:33am
Stub Mandrel wrote:

You can get little chips from Avago technologies that will put a very low current into a discharged LiON until it rises to a safe threshold and then charge normally.

Better idea than blasting with a high current IMHO.

On December 16, 2015 at 2:53pm
Caleb wrote:

If my battery pack from cordless tool was affected by water, would that cause the li ion batteries to go into hibernation mode? I looked over the circuit board and found nothing damaged. Can I bring the li ion 18650’s in this pack back to life or are they garbage?

On January 8, 2016 at 2:18pm
Ray Aguilar wrote:

Segway battery drained completely down now won’t take a charge,

On January 25, 2016 at 11:15pm
mohsen.m.shabestari wrote:

Segway battery drained completely down now won’t take a charge,

hi with all my respect
my lenovo le z500 laptop le =ion battery is in good condition capacity and other-are all
OK it coult not able to charge compactly i starts to calibrate the battery from that time it dost accept any charge and has been remain in zero charge please let me know if i can save my battery

thanks so much

On February 5, 2016 at 7:45am
Dania wrote:

Will a battery from a Bluetooth device like a headset need this boost?