lithium battery with a strange behaviour

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Joined Jan 19, 2024
Hello, I'd been trying to balance a couple of 12V 100Ah LifePO4 lithium batteries in order to put them in series to power a 24V inverter but I it seems that one of the batteries is not OK. The batteries had been used for different things before and had different state of charge.. one had 12.9V and the other 13.25V

I've read that to balance them, I needed to first charge each battery to its maximum with a 12V charger, then charge them in parallel and finally left them connected in parallel for some time.

The batteries have a maximum charge voltage of 14.5V so I bought this 3A 14.4V LifePo4 charger

When I charged them separately, one took like 30 hours but the other just like 6 hours! The charger indicates full charge with a green led. After these charges, the voltages where 13.86V and 13.98V. I though that after charging them in parallel, that 120mV difference would disappear but, after it, the difference was bigger: 13.89V and 14.24V! That was yesterday, I left them disconnected last night and today the voltages are 13.89V and 13.58V!

Is this enough to say that the battery is damaged? It has a warranty of 3 years. Does anyone have seen something like this?
Last edited:


Joined Jul 10, 2017
It would appear that one of the batteries has had considerably more use than the other. On each discharge/charge cycle, the properties of a battery change a little, until after many cycles, the battery will no longer hold a usable charge.