Restoring/Recharging Over-discharged LiPo (Lithium Polymer) Batteries!

Published

Introduction: Restoring/Recharging Over-discharged LiPo (Lithium Polymer) Batteries!

About: I'm an aerospace research engineer with a B.S. in Aeronautical Engineering and an M.S. in Mechanical Engineering. I have a *tremendous* interest in Radio Control (RC) aircraft and have developed many skills...

LiPo batteries should never be discharged below 3.0V/cell, or it may permanently damage them. Many chargers don't even allow you to charge a LiPo battery below 2.5V/cell. So, if you accidentally run your plane/car too long, you don't have your low voltage cutoff set properly in the ESC (Electronic Speed Controller), or you leave the power switch on, forget to unplug the LiPo, get your plane stuck overnight in a tree (the same tree, three separate times, for foolishly flying in areas too small because you are too excited to fly and it's almost dark), etc. etc., you may find yourself in a situation where you've discharged your LiPo down well below 3.0V/cell. What do you do?

Many people toss the LiPos in the trash. I don't. I restore them. Here's how.

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Note:

-I now maintain the most current version of this article at my website here: http://electricrcaircraftguy.com/2014/10/...

-So, if you want to read the latest version, click the link just above.

If this article interests you, you will probably enjoy this one too, so be sure to check it out!

Parallel Charging Your LiPo Batteries

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-Many additional articles can be found via the tabs at the top of the page that opens when you click the above link, and via the many links on the right-hand side.
-Links to additional articles you may like are at the very end of this instructable.
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Step 1: Background, Cautions & Warnings

Before you begin this, you need to know that LiPos are traditionally considered to be somewhat "volatile" and "dangerous."  This is because abused LiPo batteries are known to sometimes catch fire, and some have burned down houses or cars, and a fair number of Radio Controlled airplanes have caught on fire during crashes, due to damaged LiPos.  

During a reasonable or slow discharge, however, LiPos will not catch on fire, even if discharged all the way down to 0V/cell.  It is the *recharge* phase that would cause a fully discharged LiPo to catch on fire, not the discharge phase.  The reason is that when a LiPo is brought below ~3.7V/cell, its internal resistance to taking on a charge begins to increase, some of which is permanent.  Below ~3.0V/cell the damage becomes significant enough to care about.  Below ~2.5V/cell, most manufacturers of LiPo chargers have said that the battery is too dangerous to be recharged.  This is because the battery's internal resistance to charging has increased enough at this point that a standard recharge rate would be much too great for a LiPo at this low of a voltage level, since a standard 1C (1 x the battery's capacity) charge current could cause potentially unsafe heat build-up within the battery.  Below ~2.0V/cell the LiPo's rate of permanent internal damage has accelerated, below ~1.5V/cell the rate of damage (again, permanent increase in internal resistance) has increased more still, and it only gets worse and worse.  The rate at which this damage increases is not linear.  It is perhaps a power function of, or exponentially related to the battery's voltage.  In either event, it's bad, and special care must be taken.

I will now say that I have successfully restored dozens of batteries.  Some of the worst ones which I have continued to use were as low as ~1.0V/cell.  I have successfully recharged, however, batteries as low as a few mV/cell--perhaps 10mV/cell, or 0.010V/cell.  These batteries were useless, however, and rapidly self-discharged back to ~0V/cell after removing them from the charger.  

Define "restore":
Before I go on, let me define what I mean when I say that I have "restored" these LiPos.  I do NOT mean I have fixed them, or reversed their damage.  I do NOT mean I have brought them back to good-as-new.  Rather, I mean I have simply recharged them to a safe, usable level where they can continue to be used.  That is all.

A word of caution:
What I describe below is how I've restored the batteries.  Use caution.  If your battery is at 0.5V/cell, its internal resistance is far higher than if it has only fallen to 1.0V/cell, and both of these cases have internal resistances far higher still than a LiPo at 1.5V/cell.  Again, it seems to me that the relationship is *not* linear.  And remember: high internal resistance is what causes heat buildup (and potentially fires if you are not careful), during recharge.  So, if you attempt to "restore" your over-discharged LiPos, YOU take full responsibility of what happens next.  

Having said that, I've never had a problem.  The only battery that really concerned me was the one at ~0V/cell, so I really watched it carefully, and I charged it *especially* slowly.

Step 2: You'll Need a Smart Charger

I'm not going to go into the details of LiPo balancing chargers, but you'll definitely need a nice charger that can balance multi-cell packs and which has the ability to control the charge current.

Here are some links to get your started:

Note: if shipping speed and customer service are a high priority, just jump straight down to #4 in the list below to look at the Amazon prime LiPo charger options in the search results.
1) http://electricrcaircraftguy.com/2013/02/thunder-ac680-computer-data-logging.html - I highly recommend this charger; it works great and has an outstanding value. Comparable chargers to this at many other retailers cost at least 2x more.
2) Turnigy Accucel-6 50W 6A Balancer/Charger w/ accessories - also an outstanding, and dirt-cheap, yet highly functional smart charger. Excellent value; however, it requires an external power supply, such as this: Hobbyking 105W 15V/7A Switching DC Power Supply.
3) http://www.hobbyking.com/hobbyking/store/__216__408__Chargers_Accessories-Battery_Chargers.html - general list of chargers; be sure to READ THE REVIEWS!

4) And last but not least, don't forget Amazon! Here's the results for an Amazon search for "LiPo Charger". Check this list out for sure, as you get Amazon's excellent shipping speed and customer service too!

Step 3: Important Instructions Just Before You Begin Charging the Over-discharged LiPo

WARNING: during the initial restoration phase, while the LiPos are <3.0V/cell, do NOT leave them unattended. Constantly monitor them by touching them to ensure they do not get hot, and by sight/touch to ensure they do not puff up (puffing is an indication of released gases due to internal heat build-up). Once >3.0V/cell, you may place them in a fireproof charge container and continue the charge process as described in the following steps. If <3.0V/cell, I prefer to constantly feel the battery with my hand to monitor heat build-up, and I always keep a LiPo-safe charge bag nearby in case I need to throw the LiPo in the bag and run outside to let the LiPo burn in a safe area (again, never happened yet, but I don't want something bad to happen the first time there is a problem).

LiPo-safe charging bags can be purchased in many places, but Amazon always has a good selection and super fast shipping, so take a look at Amazon's search results for "LiPo charge bag" here.

Step 4: Begin the Charge (LiPo Is <3.0V/cell)

When <3.0V/cell, charge the LiPos at a significantly reduced rate of 1/20~1/10 C rate (1/20~1/10 x their capacity) until they are above 3.0V/cell. 

Example: for the LiPo battery shown at the top of this instructable, a 1/20 C charge rate would be 1/20 x 1.3Ah = 0.065A.  This is because the battery's capacity, as stated on the label, is 1300mAh (read as "mili-amp-hours"), or 1.3Ah (read as "amp-hours").  So, a 1/20 C charge rate is 1/20 of 1.3, or 0.065A.  A 1/10 C charge rate is 1/10 x 1.3 = 0.13A.  Note that although some smart chargers can charge at currents as low as 0.05A, many cannot charge at a rate lower than 0.1A.  If you cannot set your charger to charge at a current as low as you'd like, simply choose its lowest setting possible, and carefully monitor the battery during the charge.

Additional Charge Setting Notes:  recharging a LiPo below 3.0V/cell may require using a NiMh or NiCad charger setting on the LiPo batteries, as most smart chargers have safety features which prevent a user from attempting to charge a LiPo which is below 2.5V/cell, as this can be dangerous if a standard charge rate is used.  Since all we are after is setting a low (and safe) constant charge current to get the LiPo back up to a safe charge level, using a NiMH/NiCad setting is fine until we get the battery >3.0V/cell.  WHEN USING AN NIMH or NiCad SETTING TO GET THE LIPOS ABOVE 3.0V/CELL, ***NEVER*** LEAVE THEM UNATTENDED. You should not leave them unattended because the NiMh/NiCad end-of-charge detection method is not compatible with Lithium based batteries, and if left on the charger until full, the end-of-charge state will never be detected and the LiPo battery will be overcharged until it (likely) catches fire and destroys itself.

Step 5: Next Charging Steps

3.0~3.7V/cell:

Once above 3.0V/cell, you may optionally increase the charge rate to 1/10~1/5 C rate until the LiPos are ~3.7V/cell or higher.

You may stop holding the battery/constantly feeling it at this time, and place the LiPo in a fireproof container or LiPo-safe charge bag at this point, if desired.


3.7~4.2V/cell:

Once above approximately 3.7V/cell, you may optionally increase the charge rate again to 1/2 C rate until they are full (4.20V/cell).

Step 6: Back to Regular Use

Now, use the batteries as normal. The lower the battery was discharged, the more permanent damage it will have. If you use the battery (ex: to fly an RC airplane), and it works ok, then you can safely assume that subsequent charges at 1C are again acceptable. Watch it over the next few cycles, however, and ensure the battery does not puff during discharging or charging. This would be an indication that the internal resistance of the battery is still too high for normal use and standard 1C charge rates.

In any event, due to having over-discharged the LiPos, you may notice a permanent decrease in their capacity (mAh) or maximum discharge rate (ie: they will likely have a reduced discharge C-rating, as noted by lower power output & reduced performance), as the battery’s internal resistance will have been increased, and some permanent damage will exist. Additionally, the longevity of the over-discharged LiPo (ie: how many cycles you can get out of it) will have been reduced.

Let me know how this works out for you! Be safe!

Be sure to read my other articles here, especially this one:
Parallel Charging Your LiPo Batteries

I also highly recommend this one, called "The Power of Arduino."

Sincerely,

Gabriel Staples
http://ElectricRCAircraftGuy.com/

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Other Articles I've Written That You May Be Interested in Reading:

1) Parallel Charging Your LiPo Batteries
2) The Power of Arduino
3) Beginner RC Airplane Setup
4) Propeller Static & Dynamic Thrust Calculation
5) Getting into Scratch Building - 20+ Planes with ONE Motor & ONE Power Pod!
6) Thunder AC680/AC6 Charger & Computer Data-Logging Software

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    28 Discussions

    0
    user
    Stan1y

    4 years ago

    having just recovered a couple of 250mAh lipo cells from disposable e cigarettes this may be useful

    7 replies

    Awesome, tell me how it goes! Be sure to let us know what the low voltage was before you charged them up, if you recall. That info. is always good to know.

    how do I quote your ible in mine ? I'm quite new at this , the 2 batteries I've recovered so far are giving readings of 3.7V and 0.05Vand can you suggest where I read up on resticting charge current?

    Stan1y, I don't understand this question: "how do I quote your ible in mine ?".

    What's an "ible?" You mention two batteries you've "recovered." Do you mean recovered as in, "obtained," or as in "recharged?" Be careful with the 0.05V battery during recharge. To charge these types of batteries at a controlled rate, you need a smart charger. I recommend you look here: http://www.hobbyking.com/hobbyking/store/__216__408__Chargers_Accessories-Battery_Chargers.html. Also be sure to check out this article and charger here, as I highly recommend this one for its great value (value as in ratio of features to price; it has a super low price but great performance and features): http://electricrcaircraftguy.blogspot.com/2013/02/thunder-ac680-computer-data-logging.html

    under the licensing section you are supposed to give links to other instructables you modife or use so readers can check them out to I can't work out how to do this and wondered if you knew how as I obviously want to quote you as source for making my scavenged batteries useable again

    Stan1y, when you write your new article where you are citing me, please post a comment here with a link to your article. I'm interested in seeing what it's about. Thanks!

    Stan1y, thanks for wanting to properly cite my instructable; I really appreciate that. Here's how: go into the standard editor for instructables, and just above the text section you'll see a little globe with a chain link over the bottom portion of it. Hover your mouse over it and it will say "link." Create some text that you want to be the link to my instructable, then highlight it and click the "link" button. In the box that pops up, copy and paste the internet URL to my instructable, then click "ok." That's it! Feel free to use my full name and the name of my instructable. Ex: you could say, "I learned how to recharge over-discharged Lithium Polymer batteries from Gabriel Staples in his Instructable article found here: Restoring/Recharging over-discharged LiPo (Lithium Polymer) batteries!" --And using the "link" feature you could make the entire name of my article be the link to it, so people can just click on it and it will jump to my article. By highlighting the link in my comment here I was even able to click the chain button to make a link right here in my comment. Using this "link" feature I've added many links to my articles. I hope that's what you were asking. Thanks!

    Hi

    With due respect, you are wrong and this is a dangerous thing you're recommending.

    The problem with an over-discharged LiPo cell is not because the internal resistance rises... it's because once the battery is completely depleted, the lithium metal starts to plate out on the anode. This causes dendrite structures to form, which can puncture the separator, causing an internal short-circuit.

    Even if you successfully give a 'dead' LiPo a charge, that dendrite remains. You don't remove the hazard.

    A battery with a proper embedded protection circuit will have lock-out for voltages under 2.5V, in other words, it won't take a charge no matter WHAT you do to the battery (except maybe dismantle it). In the hobby world, these circuits generally aren't provided because they add weight & cost.

    There's a reason a properly designed battery charger will refuse to charge an over-discharged cell. It's not just because they wanna sell you more batteries.

    Kyle B (BS EE)

    Any idea on how to do this with fitbit charge HR's LiPo battery? its not holding charge for more than a couple of hours

    Mate, thank you very very much.

    Recovered

    GENS ACE 7200mAh 7.4V 70C 2S1P Hardcase Car LiPo Battery Pack 47#

    Amatuer RC Traxxas Slash enthusiast, left battery in unit after a hasty session in the snow. We chucked our stuff in the car and a day and half later the Lipo was down to 2.7v

    Fortunately I had a multi charger and recharged to 3.4v on NIhm setting with no heat issues at all. Switched back to Lipo balance and continued on, no dramas.

    Thanks mate, kept the fun back in RC Toys.

    Legend!

    Regards, Justin

    What about a small 70mah battery (Bluetooth ear-peace), any precautions/settings you recommend for those tiny ones or is it the same ?

    1 reply

    hey am having zippy 2200mah 3s 25c battery and my last cell has gone below 0.30v and rest is 4.12 and 4.14 and i tride to charge is shomehow i charged the last cell to 3.7v and i was not abel to charge more and i left over night and whn i saw in the morning the last cell was again 0.3v. in the last cell. the charge is not standing plz help!!!!!!

    1 reply

    If it is rapidly self-discharging that fast, it's a bad cell. The only solution is to replace the bad cell or replace the whole battery. You can carefully take the battery apart and cut out (the tabs)/desolder the bad cell. With aluminum solder and flux you can solder a new cell in place of the bad cell. The solder tabs are *aluminum* so this can be tricky and requires special *aluminum* solder and flux. Also don't short out any cells when doing it. Good luck. Attempt at your own risk, but like anything, one can learn to do it and do it properly.

    i have lipo 3s and its cell 3&1 is getting charged but not 2. why is it so?

    1 reply
    0
    user
    mcfada

    1 year ago

    Thank you! My 3s LiPo wasn't registering on my charger, I thought it was shot. A voltmeter showed it at 2.0V per cell. A quick 10-20min at 0.1A on NiMH setting got it back to 3.0V per cell, after which I was able to charge on the normal LiPo settings at 1/2C. Thanks again!

    Am I correct in that Lipo batteries don't have to be fully run down before charging to prevent damage to the memory capacity of the battery?

    1 reply

    For more knowledge on LiPos, read another one of my articles here: http://www.electricrcaircraftguy.com/2013/01/parallel-charging-your-lipo-batteries_22.html.