fuck you were faster
Perhaps, no way to say if there is actually any real difference between them once you are that low. It could be a little better to just stay with the higher voltage cells, I donāt know.
There is verrrry little data on this kind of thing in the industry and academic papers Iāve read. Everyone just says to never use cells that have dropped below 2.5V or so. An extreme view, certainly, but understandable as no one can know what the condition of any over-discharged cells actually is and liability is always on the minds of the manufacturers.
One big issue is that the longer the cells sit at below about 2.0V the greater the chance of the damage becoming a big issue. You might want to get as many cells as possible up over 2.5V to stop any more damage from occurring before trying to charge them fully. This would involve charging the entire pack or at least the p-groups instead of the individual cells (to save time).
Then pull all the cells out, let them sit for a day, and then sort them before charging them fully.
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You probably can resurrect a lot of then. Its worth a try. Also if your loop key was disconnected, it was probably the flexi, as its always listening for a can signal to turn on if I remember correctly. Also, the VESCs should go to sleep mode even if they are connected.
Unfortunately they might have been sitting low for quite a while. Could have been a week or two.
What charging current would you recommend for bringing them back?
It seems likely. Itās strange though. I had the board sitting idle before and I checked the battery periodically exactly for this reason ā to make sure the Flexi is not draining it ā and it was OK. I canāt understand why it would be any different now. I didnāt change any settings. Could be a Flexi bug.
If you suspect it was a bug then I would get in touch with Simo via email.
I have no idea. 
Slower is better but takes longer to get your cells back up over 2.5V. Definitely not over 0.5A/cell IMO. If charging the entire pack then perhaps try 0.1A/cell. The low charge rate will take a while to get them over 2.5V but itās safer and youāll be charging all the cells at once (saving time).
Check cell voltages and temps oftenā¦very often.
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Right. Iāll let him know though I donāt think heāll be able to do much about it. Thereās not even clear evidence the Flexi was the culprit here.
Iāll take the battery pack apart but will keep the P-groups assembled and then try charging maybe at 1A (these are 7P groups). Will do one of the better groups first and see how it goes. Iāll keep you posted. Thanks for the help and encouragement. You guys are great.
In return, I may later send you some funny videos from my security camera showing me panicking around a NESE p-group on flames, desperately trying to find a way to get it out of the window.
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awe man Iād hate love to see that video!
Itās always disturbing to realize how amusing I find videos like those. If I was in that situation there would be absolutely nothing amusing about it at all. 
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yet you just know that seeing anyone else in that situation is at least a little amusing, if not scary and sad. a full gamut of emotions for your serotonin needs.
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hissssssss
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I would at least bring it up to nominal voltage, not just 3v
The risk is 1 cell taking more current than the other charging in parallel and testing in parallel can give you false confidence. Your testing a average you need to know if one is not charging been disguised by the others. Heat is going to be your biggest clue charging like that. Keep touching them if the temp comes up un evenly stop same with keep the temps way down
Isnāt it more risky in case things go wrong? More voltage = more fireworks?
Iām well aware. I may take the P-groups apart later and do more testing. From what understand, itās important to bring the cells back to the safe voltage quickly and if I do it one by one it will take me a week.
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I just know Li-Ion cells like to be at their nominal voltage, any less risks damage and anything more risks explosive decompression (fireworks)
additionally, you want to make sure your cells will recharge to at least their nominal voltage.