4 batteries 48v problem at night

I have 4 battles of 12v connected in series to obtain 48v everything its been almost perfect for a few month but recently at day the batteries work great but at night the console say the batteries are at 0v and when i check the batteries individually 3 batteries have the 12volt but the battery that have the positive cable connected to the controller and inverter its say negative 36v this battery have the negative cable that goes to one of the other batteries and in the positive connection it have the positive cable that goes like i say to the all in one inverter that i use.

Help pleaseeeee

Measure each battery separate and post the voltages. Disconnect and separate if needed.
Are these lithium batteries?

Yes they are lithium batteries and 3 of them always say 11 to 12 volts but one say negative 36 i read something about reverse charge at that’s why that battery say negative 36 because its the the voltage of the other 3 batteries 3x12= 36 but I don’t know why this happened and even if i change the batteries positions the error appear again so its not a battery problem

Is it likely that one of the batteries is experiencing more discharge than the rest?

I would second the recommendation to disconnect the batteries and measure each one individually.

I would guess that the battery currently showing -36 volts actually has a BMS that faulted and opened/disconnected.

lowrads said:

Is it likely that one of the batteries is experiencing more discharge than the rest?

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I don’t think that possible because they are in series connected

400bird said:

I would second the recommendation to disconnect the batteries and measure each one individually.

I would guess that the battery currently showing -36 volts actually has a BMS that faulted and opened/disconnected.

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That show 12 volts if i test them together 3 say 12 volts and one -36 and if i disconnect them 3 still saying 12 volts and the other one say 0

This only happens at night because in the day they work perfect

Sounds like your one battery is having issues and dies quick when it looses solar....

Just my guess though.

dmitrimedina said:

Yes they are lithium batteries and 3 of them always say 11 to 12 volts but one say negative 36 i read something about reverse charge at that’s why that battery say negative 36 because its the the voltage of the other 3 batteries 3x12= 36 but I don’t know why this happened and even if i change the batteries positions the error appear again so its not a battery problem

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Happen to have a pic and perhaps a technical description of your battery bank (and BMSs)?

Put a 12v charger on all of them. If that battery is really -36 volts it is not a 12 volt battery. No way to put any 12 volt battery to 36 volts and not be smoking hot or exploded.

Noob here, but I've seen exactly this issue on a mates small 48V system.

The same 4 x 12V LiFePO4 batteries in series.

At night the packs discharge until the "lowest" pack shuts off on under-voltage killing the whole arrangement.
During charging the "highest" pack shuts of on over-volt before the "lowest" has had chance to get charged.

Over several months the packs get more and more out of balance with each other.

Solution, balance the packs. Disconnect the lot and charge each pack individually. Then connect them all in parallel and give them a slow charge over night. That should get them back into some semblance of balance.

Of course, if you have a "weak" battery (his are used so heaven knows what life they've had) they will go out of balance again. He just uses a 12V charger every month or so to "help" his weaker battery.