![]() 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. Having said that, I've never had a problem. So, if you attempt to "restore" your over-discharged LiPos, YOU take full responsibility of what happens next. And remember: high internal resistance is what causes heat buildup (and potentially fires if you are not careful), during recharge. Again, it seems to me that the relationship is *not* linear. 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. A word of caution: What I describe below is how I've restored the batteries. ![]() Rather, I mean I have simply recharged them to a safe, usable level where they can continue to be used. I do NOT mean I have brought them back to good-as-new. I do NOT mean I have fixed them, or reversed their damage. ![]() Define "restore": Before I go on, let me define what I mean when I say that I have "restored" these LiPos. These batteries were useless, however, and rapidly self-discharged back to ~0V/cell after removing them from the charger. I have successfully recharged, however, batteries as low as a few mV/cell-perhaps 10mV/cell, or 0.010V/cell. Some of the worst ones which I have continued to use were as low as ~1.0V/cell. I will now say that I have successfully restored dozens of batteries. In either event, it's bad, and special care must be taken. It is perhaps a power function of, or exponentially related to the battery's voltage. The rate at which this damage increases is not linear. 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. 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 ~2.5V/cell, most manufacturers of LiPo chargers have said that the battery is too dangerous to be recharged. Below ~3.0V/cell the damage becomes significant enough to care about. 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. ![]() It is the *recharge* phase that would cause a fully discharged LiPo to catch on fire, not the discharge phase. During a reasonable or slow discharge, however, LiPos will not catch on fire, even if discharged all the way down to 0V/cell. =īefore 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. Links to additional articles you may like are at the very end of this instructable. 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. Also, please subscribe to my site via the icons at the top-right when you click the link above. If this article interests you, you will probably enjoy this one too, so be sure to check it out! So, if you want to read the latest version, click the link just above. I now maintain the most current version of this article at my website here: What do you do? Many people toss the LiPos in the trash. etc., you may find yourself in a situation where you've discharged your LiPo down well below 3.0V/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. Many chargers don't even allow you to charge a LiPo battery below 2.5V/cell. LiPo batteries should never be discharged below 3.0V/cell, or it may permanently damage them.
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