I successfully brought several P-groups above 2.5V without any issues whatsover. So I gained some confidence and connected 3 groups in series so that I can charge faster. But my charger is like: “Bro, this ain’t no 3S. Even if it was 2S, at 2.97V total that would be pretty fucked. I’m not buying this bullshit.”
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I’m not insisting that I’m right, just suggesting that I might be.
Yeah my “smart” charger won’t start charging my flexi bms pack, because the flexi disables the charge port when it’s not in use. The charger then sees no voltage and thinks its not connected. 
This isn’t true.
Our “standard” li-ion cells are rated down to 2.5V for every cycle and can be held at that level without damaging the cells. However, you then risk the inevitable slow self-discharge bringing the cell down to below 2.5V. This can lead to accelerated aging and, eventually, possible damage to the cell.
Anything up to 4.20V also isn’t a safety issue but there is faster and faster aging as the voltage gets higher and higher.
The nominal voltage is a convenient place to leave a cell for long term storage but cells are now being left at 30% charge when manufactured since that leaves less energy in the cell to cause trouble if it is shorted or damaged in transit or storage. This is in the 3.35V-3.45V range IMO. The manufacturers would not do this if it damaged the cells.
“Explosive decompression”?
Umm…this won’t happen at above the nominal voltage, up to 4.2V/cell. 
Just a phrase you used? Cells can go higher than that, of course, but the damage and risk rises quickly.
No need to, especially since that can take a long time and what’s needed now is getting his cells all back over 2.5V ASAP. A slow charge to the nominal voltage, roughly 50% charge, will take a much longer time and isn’t necessary to help prevent the damage that is possibly occurring from being below 2.0V-2.5V.
After all the cells have been pulled up over 2.5V he can look for “leakers” (ones that self-discharge quickly) and then charge them back up to a level he can test them at (nominal voltage, full voltage, wherever).
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I lost a 16s4p p42a pack this morning bc I left the Ubox on all weekend. Drained to less than 1v/cell.
About to finish the replacement by the end of the day today.
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I had ~0.5V / cell this morning and I made decent progress with the recovery.
Out of the 12 P-groups, I managed to get 11 above 2.5V. I charged slowly at 0.1 A per cell (0.7 A per P-group) as suggested by @Battery_Mooch. It went smoothly. Nothing was getting hot.
I monitored the voltages afterwards and none of the P-groups was loosing charge (other than minor decrease in voltage, which is normal after finishing charging). I wrote all the voltages down and will check again in the morning.
I wasn’t able to recover the worst P-group, which got drained under 0.1V. I didn’t even know how to charge it since the iMax charger refused to charge due to low voltage and I don’t have any adjustable constant current power supply (I should really get myself a laboratory power supply). I tried charging one cell with a buck converter that I set to 1.2V but that didn’t work. I’ll just discard this one P-group and get 7 fresh cells. If that’s the worst thing I have to do that’s still a pretty good outcome.
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I’m gonna give my dead pack to @TheRef , if he recovers it he’ll give me $50 haha
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The bends.
Hoists the sails and begins a shanty
OoOoOooOoh heave her up and away we’ll go, away Santiana! Heave her up and away we’ll go along the plains of Mexico!
Cells explode
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I have safe places to experiment and try to recover them
No I’m just horrible at videos 
maybe I’ll chat with the one wheeler.
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Shouldn’t the Ubox shut off automatically? 
nope
ubox doesnt have an antispark, instead it has a power switch that just puts it to sleep 
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It should go to sleep automatically, but it didnt. I never programmed it to.
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What I have found to be a bit easier to do in these areas is to have two solder points, connected with a small piece of braid as a bus, then the end of the lead on one of the solder points. It functions the same, and eliminates having to deal with many strands or multiple insulation gaps in the wire.
And since you’re using braid already it’d just be an extra couple pieces.
Food for thought, at any rate.
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When I’ve done these I used one 10awg pre twisted and tinned, the soldered it onto the nickel, also pretinned, before welding it to the pack
Seems to work out alright. The charge wire I attached somewhere else on the strip - this strip could have been a bit longer it seems - still perfectly functional though
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That should really be the default 
Now that I think about it, i might have experienced the same when I first got my Ubox, only that I flashed it two days after…
Why is this the first we are hearing of this lol @jack.luis
I’ve never heard of this either
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It’s a pretty cool feature, I always wondered why the fishpaper ring wasn’t just a part of the cell lol
(yes I know some battery building techniques take + and - from the top)
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