Pulled cells from 2 fujitsu-siemens laptop packs, 14.4v 8 cells.
All cells ranging from 3.2-3.85v.
Started charging 1 battery in my ML-102 and 2 in my WF-139.
All 3 were at around 3.6v.
Checked them after a while and the battery in the ML-102 felt really warm so I pulled it from the charger, thinking I’d charge it in the wf-139 together with another battery as it only would get 500ma then instead of 1000ma.
It was at 3.9v.
The cells in the wf-139 were lukewarm.
Later checked the wf-139 again and the batteries were on the verge of being too hot to hold…. Of course the charger were pretty warm too so I stopped charging.
Both cells were at around 4.1v, checked them now a couple of hours later and the resting voltage is just above 4v.
li-ion cells should never get warm while charging. If they do, recycle them. Sorry about the duff find, sometimes you win, sometimes you recycle
Also, if any cell drops more than 0.1V sitting around in a week, it’s no good either. Given that yours did that in a couple of hours I doubt they would be much use even if they charged fine.
With that much voltage loss in that amount of time I would toss them. Li-ions do go poof when heat builds up. At the same time pressure builds in the cell. That’s the reason a lot of manufactures install a vent, its a pressure vent . If you had left it on the charger and it keep building heat it could have possible went poof with flames.
That’s the crappy part about pulling cells from laptop batteries, they rarely are all on good working condition.
Just test all of them (by test I mean charge to see if they get hot) and put the ones that get hot in the garbage.
The odds are tipping in favor of bad cells. I suppose the heat is caused by low cell voltage or high internal resistance or both, depending on the charger protocol.
If you have enough cells and chargers and time you almost don’t need a multimeter, but with a meter and by simulating a cell with a hefty Zener diode and a power resistor you could be more certain of what is bad or good.
