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Recovered over-discharged lipo from over a year ago!

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I wasn't sure about how I'd like to approach this topic, given the intrinsic dangers of Lipo batteries. But hopefully readers will have enough criterion on how to take the following anecdote

Disclaimer: This is no way a how-to, tutorial or a "green light" on recovering your overdischarged lipos; as usual, I'm just sharing my experience in this forum which has been one of my primary sources of information since I started on this hobby.

-= If you want to skip the boring backstory feel free to skip to the part with Bold letters

So, a year ago I made the mistake of leaving the Typhoon H on (motors off), waiting for it to discharge a battery to "safe levels". I completely forgot about it and when I went to check the aircraft was already off, and the battery wouldn't charge; the carger would give a series of long beeps while flashing a blue light: Error

I looked around for some advice, and even posted here if it was possible to recover the battery. Sooner than later I got that consensus was: Battery is damaged, the best option is to purchase a new one.

Actually, here is the thread I posted on this forum, back on Sep 25 2016 Fully discharged battery, is it savageable?

I followed the general advise, stopped trying to save it and purchased 2 extra batteries after that. However for some reason I was reluctant to plainly discard the old battery.. I thought: "it should be good for something.." (also I'm kind of a hoarder; I mean, I still keep all my broken props) So I went ahead and put it somewhere safe and stored it.

All this time, the issue of recovering overdischarged lipos had me wondering: "could I ever recover that battery?" I knew it was no longer to be trusted, and even if I were to "recover" it, I should not use it normally as I would use my regular batteries.

Every now and then I was reminded of the topic so I started a continious research about it finding surprisingly different opinions on different boards: Some users were extremely cool about it "Yeah, its ok go ahead" while others' opinions could be resumed as: "Recharging OD'd Lipos = death". All this information was very interesting and useful to develp a personal perspective about the Lipo batteries, keeping in mind that I should be careful to differentiate facts from opinions. (specially when planning on doing something dangerous, literally playing with fire)

I didn't have any other charger than the stock one, and I think this helped me to perform a very deep thorough research, since I didn't have the means to try it by myself even if I wanted to.

Anyway, a few weeks ago I started researching on Smart chargers, not really thinking about the "dead" battery, but I decided I would invest in one to take better care of my batteries given the stock charger has severely limited functions (basically one: charge)

At the same time I started looking at the different brands of chargers I also went back on researching the Lipos themselves again to really understand their operation and what I needed: "How do Lipos work? What does C-rating means? What is internal resistance? Why charge at 1Amp or 5Amp? What is an Amp? etc, etc etc..." Now that I wanted to monitor them more closely I wanted to make sure I at least had some idea of what I would be looking at.

So finally, I purchased my new charger and I have to tell you, I'm so glad I finally got it! It's not the cheapest nor it is the most expensive or fancy charger out there, but after a lot of research I'm sure its definitely the one that best meets my needs, and it will definitely help me extend the life of my batteries.

Now, this is the part that bugged me the most upon deciding if I should post this thread: It is said that not only the lowest the battery has been discharged but also the longer a battery has been at that state, the greater the permanent damage it will have (considering that at low voltage the battery will tend to keep draining over time). So, I am very well aware of what I was getting into. Again, It's not like I was handling TNT, but I was ready for a potential lipo fire.

Long story short (not really short is it?) I was able to bring back the 1-year-long overdischarged battery!

The recovery proces was slow.. and I mean slooooooow, and for the most part this was deliberate as I didn't want to rush anything eventhough I knew it was possible that the lipo was completely inert after all that time or that it could ignite without warning.

I never got to measure the voltage of the battery after I overdischarged it; once I set it back on the aircraft and it had enough power to give the first Beep and turn on the lights for a second but then it went out, the charger wouldn't charge at all.
Literally a year later, now with my recently acquired charger, I was able to take a better look at the battery, and the things that I initially saw where a little bit concerning:

First, I wasn't getting any voltage from any cell, I mean it showed absolute 0.00V on each of the 4 cells, but then the general voltage showed around 6.5V, meaning the individual reading was just undefined and not really zero.
Second, I wasn't getting any internal resistance reading from the individual cells either, however the overall IR read about 130mΩ (!)

After knowing a bit more about the status of my battery I went out on a research again considering the specifics of my battery, not only the readouts but the fact that it was very Slowly discharged and it showed absolutely no signs of puffing.

When I say the recovery (recharge) process was slow I mean it took me about 12 hours of, constant voltage monitoring, temperature and visual inspection looking for Any kind of puffing, internal resistance measuring every half an hour or so, and obviously keeping the battery inside a safety lipo bag and a clear way outside in case things got ugly. (didn't have an extinguisher though)

After a whole day invested I was able to take it close to a full charge (didn't really reach 4.20V per cell), proceeded to leave the battery inside the Safety Lipo bag overnight, and rechecked Voltage 12 hours later.
Surprisingly the pack held all the voltage overnight. (Forgot to mention IR values normalized soon after increasing voltage during the first hours of recharge)

Today I decided to test it on the aircraft under moderate load, also making regular pauses to inspect the battery, checking temperature, and signs of puffing. I kept the unit close to me and was ready to react in case the aircraft started to smoke or if it blacked out in mid-air.

Happy to say the battery is working! Flight time must have been reduced but I can't really tell how much after this initial test. I still have to perform more tests to get a feel of the battery's performance/reliability. Obviously I've labeled the battery as a recovery, meaning I wont use it normally as the other ones and will always consider it unstable.

Anyway, this was a very exciting experience for me. I know this isn't the first time anyone has recovered an overdischarged battery so this isnt a "groundbreaking" topic. And even if the battery isn't in a good-as-new state, I definitely learned a lot from this. I'm not going to describe the step-by-step process, as I mentioned this wasn't meant to be a tutorial or a how-to recover OD'd lipos. If you wish to perform this procedure there's a lot of information out there, and also lots and lots of warnings that I'm sure are very well justified. (youtube search lipo fires and consider if you're willing to deal with that inside your house)

Even though I was able to recover this battery, I still believe the best thing to do after overdischarging the battery is to get a replacement; the whole recovery process is slow, it is not guaranteed and its a fire hazard. It can be done, but a new well-maintained battery will always be best.

I've researched about the Lipo batteries but I am by no means an expert, I still have a lot to learn!

Anyway I hope you enjoyed the long read :D

Greetings!
 
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Steve Carr

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Regardless of the outcome it's a fun project. You were very deliberate and cautious in your approach and that alone is commendable. Thanks for sharing your story.
 
R

Rayray

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I did enjoy reading that, although I commonly read quite a bit. About a year ago I had a battery go down to just over 12 volts, which the stock charger would not charge--love that blue light. Another charger did charge it, and now it's in the rotation I use. Yours at zero I'm sure I would have not bothered with.
Take care...
 
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PatR

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Good job and nice report. Having done similar with over discharged batteries I hope you have better luck with yours than I have. Mine will achieve full voltage charge values but provide significantly reduced duration under load.
 
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Nice job, good information for sure. I just picked up a HiTec charger and ordered the adapter for the H batteries. I am really interested in seeing if this new charger does better. Thanks for sharing.
 

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