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Discussion Starter · #1 ·
I'm carefully looking into the best re-use scenario for lithium NMC pouch 57ah 3.7v nominal 31s modules/cells. I'm going to eventually pull out the bad cells, fill space to maintain original orientation, and reconfigure. And then potentially I may decide to use an appropriate Chinese bluetooth bms, and put into service, for stationary use. This "experiment" is taking place in a detached shed with appropriate fire suppression on hand, and all other safety precautions being followed.

I'm charging at extremely low amperage (.01,.05a) at module level upto maybe ~70V(3.1v/cell)...(at first), and also balancing and charging individual cells with either lab power supply, imax b6 hobby charger, active balance board, appropriate resistor/load, or other methods, incrementally. I am actively monitoring cell temperatures and would stop if any cells were to get warm (but at these extremely low amp trickle charge levels even the bad cells have not been heating up at all). I am recording voltages and monitoring initial voltage drop of every cell after taking off the charger.

When I find a module with (seemingly) bad cell, which is not taking a charge, I stop. I try to charge that cell individually upto ~2.5-3v (.01, .05a) and (in the case of the bad cells), they will either:
1) raise in voltage a little or seemingly pretty normally take a charge but then drop within an hour to almost 0v , or maybe ~.5V range.

2) not take any charge at all, maybe they will show some voltage while charging, but they will not hold it for any significant amount of time, basically totally dead 0v-.08v.
3) Also, some (occasional) cells will take a charge but then the initial self-discharge is much more significant than 10%

I have lots of experience with 1850 cells and electronics/cell phone type pouch cells, and have come across some of those types in used electronics etc who's cells have either expanded or lightly vented/etc, but I've not experienced any type of venting or thermal runaway myself, directly.

I've seen people on youtube charging a whole module with a bad cell/cells, all the way up to the nominal or close to full pack voltage, but I'm not going to do that, (am I being overly cautious ??) ...once I've identified bad cells, I'm going to pull them out, and then continue trickle charging and balancing the smaller reconfigured module in increments (2.1v, 2.5v,3v,3.2v etc to 70%).

I'm trickle charging at low amperages just simply to be overly cautious, and I am giving them sufficient time .....(.01, .05, .07a, at module or cell level and appropriate voltage), max I've tried on these seemingly bad cells so far has been .1a-.2a.

I'm curious if anyone would be willing to share their insights, experiences or advice into the different "failure modes" & what's happening with the types of "bad" cells I've described above, any further testing I should be doing on these bad cells (maybe I just haven't increased the amperage enough, cell level charging, even though I've given them sufficient time at extremely low amperage?), and your thoughts on continuing to charge up or temporarily storing (not using) a module that has bad cell/s (either ~0v, or high initial discharge) to/at maybe the 3v, 3.2v, 3.7v per cell...
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