Is my battery bad? Can it be fixed temporarily?

[lifeontheroad]

Here's my battery setup 4 81ah batteries in 2s2p.
The problem: one of the batteries reads 11.58 volts and the others hover around 13.6

Can this be fixed or is it a goner?
Should I get a replacement or will it hold on until a get a 24v lithium battery

 

[v_green57]

So, should we assume you disconnected all the jumpers and measured them individually?

 

[Overmind]

Dismount all of them, connect them in parallel and see if the one with low voltage recovers. Disconnect them once they get to 12.6V or around there and check if the assumed to be bad one keeps that voltage or drops back low lower values.
Alternatively, manually charge the low voltage one to the value of the others and observe the same effect.

 

[Vigo]

Since the missing voltage is suspiciously close to 2.1v, it is somewhat likely that you have a dead cell in that battery. If you are able to check SG or have any form of load tester (the 50/100amp one they sell at harbor freight for $20 is fine) you should be able to determine that very quickly, much more quickly than rewiring them to parallel and simply waiting.

Another thing you could try quickly is just popping the vent caps off the low battery, hooking a 12v charger to it at a high current rate, and see if one of the cells bubbles much less than the others. That would be an inexact but immediate sign of a cell problem.

If an equalization charge does not fix that battery, it is ready to recycle.