Rescuing a 100Ah LiFePo4

[@Michael]

I have a 100Ah Battleborn that's been sitting unused for a couple years. I charged & discharged it periodically to keep it healthy - putting a small load on it for a bit, then charging it to 14.4v and disconnecting the charger.

Last fall I bought a cheap capacity tester and found its capacity to be less than 50% (490 watt-hours).

I played around a bit and found out that if I charge to a voltage just above where the battery acceptance rate slows down and then hold the voltage at that value, the battery will draw a small amount of current (.170 amp) for a long period of time - from several days up to a week - before tapering to zero amps.

Each time I repeated the charge & hold cycle at a slightly higher voltage, the tested battery capacity increased by a few hundred watt-hours.

I.E - from an initial capacity of 490 watt-hours:

• Charge to 14.0v, hold until .170a current draw drops to zero (several days). Tested capacity = 700wh
• Charge to 14.2v, hold until .170a current draw drops to zero (several days). Tested capacity = 900wh
• Charge to 14.3v, hold until .170a current draw drops to zero (several days). Tested capacity = 1150wh

I'm speculating that the battery cells were far out of balance and that when charging to 14.4v I was hitting a high voltage threshold on some of the cells before the balancer could pull up the lowest cells, and when discharging I was hitting a low voltage threshold on other cells. By working the voltage up incrementally the internal cell balancers are able to bring up the low cells without the highest cells tripping a high voltage threshold. The .170a current draw is from the passive cell balancer.

I have no idea if the battery is permanently damaged or not - I.E. will it continue to test at near full capacity over time or not.

I guess I'll find out.

[booster]

Originally Posted by @Michael

I have a 100Ah Battleborn that's been sitting unused for a couple years. I charged & discharged it periodically to keep it healthy - putting a small load on it for a bit, then charging it to 14.4v and disconnecting the charger.

Last fall I bought a cheap capacity tester and found its capacity to be less than 50% (490 watt-hours).

I played around a bit and found out that if I charge to a voltage just above where the battery acceptance rate slows down and then hold the voltage at that value, the battery will draw a small amount of current (.170 amp) for a long period of time - from several days up to a week - before tapering to zero amps.

Each time I repeated the charge & hold cycle at a slightly higher voltage, the tested battery capacity increased by a few hundred watt-hours.

I.E - from an initial capacity of 490 watt-hours:

• Charge to 14.0v, hold until .170a current draw drops to zero (several days). Tested capacity = 700wh
• Charge to 14.2v, hold until .170a current draw drops to zero (several days). Tested capacity = 900wh
• Charge to 14.3v, hold until .170a current draw drops to zero (several days). Tested capacity = 1150wh

I'm speculating that the battery cells were far out of balance and that when charging to 14.4v I was hitting a high voltage threshold on some of the cells before the balancer could pull up the lowest cells, and when discharging I was hitting a low voltage threshold on other cells. By working the voltage up incrementally the internal cell balancers are able to bring up the low cells without the highest cells tripping a high voltage threshold. The .170a current draw is from the passive cell balancer.

I have no idea if the battery is permanently damaged or not - I.E. will it continue to test at near full capacity over time or not.

I guess I'll find out.

I think you are correct in what you think is going on, and it sounds similar to other Battleborns we have heard about. Lost capacity from out of balance.


I can't say for sure, but perhaps the Battleborns go out of balance more easily than other lithium batteries do. It appears that you would probably need to charge to full more often to get them balanced and keep them there.


So far, we have been lucky in that we never charge to full on our 3 parallel SOK batteries and they have stayed in balance for about 1.5 years so far with never have been being balanced except when new, when I opened them up and balanced the cells individually.