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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

-Also, please subscribe to my site via the icons at the top-right when you click the link above.
-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

having just recovered a couple of 250mAh lipo cells from disposable e cigarettes this may be useful
<p>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.</p>
<p>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?</p>
<p>Stan1y, I don't understand this question: &quot;how do I quote your ible in mine ?&quot;.</p><p>What's an &quot;ible?&quot; You mention two batteries you've &quot;recovered.&quot; Do you mean recovered as in, &quot;obtained,&quot; or as in &quot;recharged?&quot; 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</p>
<p>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</p>
<p>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!</p>
<p>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 &quot;link.&quot; Create some text that you want to be the link to my instructable, then highlight it and click the &quot;link&quot; button. In the box that pops up, copy and paste the internet URL to my instructable, then click &quot;ok.&quot; That's it! Feel free to use my full name and the name of my instructable. Ex: you could say, &quot;I learned how to recharge over-discharged Lithium Polymer batteries from Gabriel Staples in his Instructable article found here: <a href="https://www.instructables.com/id/Restoring-over-discharged-LiPo-Lithium-Polymer-bat/" rel="nofollow">Restoring/Recharging over-discharged LiPo (Lithium Polymer) batteries!</a>&quot; --And using the &quot;link&quot; 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 &quot;link&quot; feature I've added many links to my articles. I hope that's what you were asking. Thanks!</p>
<p>I just added a new Step 2 in my article, which contains a few charger links.</p>
<p>i have lipo 3s and its cell 3&amp;1 is getting charged but not 2. why is it so?</p>
<p>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!</p>
<p>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?</p>
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.
Yes, you are correct. NiCad batteries have the memory effect. NiMH do too, but not as bad. Precharged/Low Self-Discharge NiMh have it even less, and LiPo don't have it. As a matter of fact, you'll maximize the life of a LiPo by NOT discharging it all the way. LiPos are happiest (suffer the least wear) in the 20% to 80% full range.
<p>My 2200mAh 30C 3S battery had discharged just one cell to 0.05V and the other two cells seems to be okay</p><p>I only have a balance charger not a NiMH</p><p>What can you suggest ?</p>
First, verify with a plain multimeter (not a cell checker) that the cell really did get down to 0.05V. Looking at the balance lead for a 3S LiPo you have 4 leads, as follows: (-)1--2--3--4(+), where if you measure from 1 to 4 you get the voltage of the whole battery--same as measuring the main leads. From 1 to 2 you get Cell 1, from 2 to 3 you have Cell 2, and from 3 to 4 you have Cell 3. This is because all the cells are in series. So, use your multimeter and determine if the cell really is that low. If it is that low, that cell is worthless--no sense in trying to &quot;restore&quot; it. Just desolder/cut out that bad cell. When I say cut it out, I do NOT mean cut the pouch, I mean cut the lead to it. Literally, *carefully*--either outside the house, or with LiPo fire-safe bag nearby, remove the wrapper from the battery, and without shorting anything, cut out that bad cell. Now, If the cell from 2 to 3 is bad, for instance, you'll need to jumper from 2 to 3 with a wire. I don't have an open battery in front of me right now to verify my instructions make perfect sense, but you should get the point: you'll need to make sure you have the remaining cells in series still. You'll also need to carefully remove the wires (by lifting with a pin or X-acto blade tip the plastic retainer) from the balance leads, as necessary, to keep all balance leads in series properly still too. When done, carefully tape, wrap, and heat shrink the whole battery pack back together. Now you'll have a 2S LiPo to use instead of a 3S LiPo. Alternatively, you can find individual cells from HobbyKing and solder in a new cell. A word of caution though for working with LiPo cells: the soldered cell tabs are brittle, and *aluminum*. Use a separate solder tip (to not ruin your main tip), and you'll need special aluminum solder and aluminum solder paste/flux to solder aluminum. Good luck!
<p>Thank you very much for this Instructable! Thanks to you I was able to revive my brothers tablet.</p>
<p>Very nice choice of airplane.</p>
<p>Hi there!</p><p>Thank you for your instructable on restoring lipo batteries. I have a very tiny lipo battery from a medical device which doesn't seem to take charge. Here's a picture of it:<a href="https://www.google.com.au/search?q=pp312122AB&rlz=1C2CHFX_enAU604AU604&biw=1366&bih=667&source=lnms&tbm=isch&sa=X&ei=JDg7VJTsAYXu8gXQxoHABA&ved=0CAYQ_AUoAQ#facrc=_&imgdii=_&imgrc=ZED334fJzQjYXM%253A%3BiHpcGu3_6c_RUM%3Bhttp%253A%252F%252Fi01.i.aliimg.com%252Fimg%252Fpb%252F236%252F578%252F562%252F562578236_838.jpg%3Bhttp%253A%252F%252Fwww.aliexpress.com%252Fstore%252Fproduct%252FPP312122AB-3-7V-Li-polymer-Rechargeable-Battery-1pcs-lot-free-shipping%252F318150_737169824.html%3B800%3B800" rel="nofollow">https://www.google.com.au/search?q=pp312122AB&amp;rlz=...</a></p><p>All I know it's a 3.7V battery. It measures 2mm by 20mm by 20mm. Unfortunately, one is not available for sale and a replacement would also be hard to find. So I'm wondering whether it can be restored. Because it's supposed to be charged for 3 hours and the writing on the charges says 5V-0.5A, I worked out that the capacity of the battery is 0.5A X 3 = 1.5Ah. However, I cannot imagine such a small battery having such a large capacity. Usually batteries of this size have a capacity not exceeding 0.1Ah. I know that my only chance of restoring this battery is using a mini-charger which can produce currents as low as 10mAh.</p><p>Moreover, the wires from the battery seem to be soldered onto the electronics board, rather than connected. I would imagine that to connect the wires to a charger of any sort, I would have to break off the wires and fit them into a JST plug, which is another thing I don't know how to do. Finally, when it comes to soldering the wires back on, the whole thing is on such a micro scale that even if I was familiar with soldering (which I'm not), there would be a great risk of damaging the electronics board. Do I have a chance of recharging this battery?</p><p>Thanks!</p><p>Kind regards,</p><p>tolerant</p>
<p>Hi great question. I just posted a lengthy answer to your question in the comments under my article here: <a href="http://electricrcaircraftguy.blogspot.com/2014/10/restoring-over-discharged-LiPos.html" rel="nofollow">http://electricrcaircraftguy.blogspot.com/2014/10/restoring-over-discharged-LiPos.html</a></p>
<p>By the way, the micro LiPo charger I was talking about is this one: http://www.leobodnar.com/shop/index.php?main_page=product_info&amp;products_id=215</p>

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