The bad battery had gotten "puffy", which is the death knell of LiPo batteries. The other was starting to get puffy but hadn't gotten too bad yet...
This sounds like the batteries are being over charged. A very bad condition for any Li battery (look on youtube for overcharging).
How do you charge this devious? I suspect that your charger is at fault and this will take out the replacement battery too.
Don't Li-Ion batteries have a protection circuit built into the battery pack? I thought this was mandatory due to the high risk of fire or explosion.
(sorry for the long story)
That answer can go both ways. The reason why I asked, how do you charge them?
I'm reading/looking into Li batteries. Going to make a few battery packs. If the batteries are stand alone, you can over/under charge then, run them down to zero v, and then you kill it, over charge, and blow them up.
You're referring to a BMS (battery maintenance system), which usually has an over/under protection circuit. The max V on a Li-ion is 4.2V, I think the lowest is 3.2V, with nominal charged voltage is 3.7V. By going through your BMS, it turns off the battery pack when a cell gets to 3.2V, and when charging, if a cell reaches a high above 4.2V it turns it off from the charger and starts to drain it (putting it into a loop).
But you can charge your battery in a charger, that has a built in BMS, then take the battery to a device and plug it in. Hopefully it turns off when the voltage reaches the 3.2V (it can get very complicated here, so I'll leave it as a single cell).
Usually you have batteries in a series, 3 Li-ion at a low of 3.2V x 3 (9.6V) to a high of 4.2V x 3 (12.6V), so the device it's plugged into wants a working voltage 10-13V. When the batteries drain to the 10V it turns off, you can't use the batteries any longer. Look at your electronic devices, they say they want a voltage range from the charger, so any steady transformer with the above voltage within 10-13V would work in the above example.
My 12V LiFePO4 motorcycle battery, I feel does not have a BMS in it. It's strictly a battery cell. I can plug in a remote BMS charger, which cost me $80, and charge it up. When I put it in the bike, the max voltage coming from the alternator is 14.2V, which is in range. The bike will possibly die when I get down to a sub 10V charge. But if I was to leave the lights on, I could drain the battery to 0V, and the battery may not recover from a sub 9.6V discharge.
I have batteries waiting for me to pick up in the US, but the border is closed. When I do, I'll be making a BMS controlled LiFePO4 and a Li-ion motorcycle battery, and posting the project here, and maybe in youtube. These can be very small and light weight batteries, like the little jump start cells.
Also, my LiFePO4 mc battery, is wired for a GW, pos/neg on the revers side. Since I'm not using it, I'm going to somehow take the top off, and flip the batteries around inside to revers the voltage polarity, to make it usable in my Valk.
