Q: how do I upgrade an old, semi-functional battery pack?

System

A friend of mine has an off-grid solar (12v w/ automatic diesel backup) set-up. The first two battery banks are almost dead (they only lasted 4-5 years each).

I figure many of the 6v batteries will have a dead cell. Can I wire these in series of 3 (4v) batteries, so they have additional useful life? or will this be unsuccessful?

Also, I'm planning upon selecting the working 6v batteries and making sure they aren't in series with a "dead" battery.

Any suggestions?

Cariboocoot

Re: Q: how do I upgrade an old, semi-functional battery pack?

As a general rule, any battery that has one bad cell - the others will be close behind in failure. There's really no way to salvage batteries that are gone, except to sell them as scrap and put the money towards new ones.

The only possible "saving" of a battery is to try and equalize the cells, if you have a charge source capable of that function. Get a good specific gravity reading before you try; too low or too far apart and there's no sense trying.

As for re-wiring the cells, it would depend on the specific batteries as to how accessible the individual cells are. If there aren't inter-cell connections visible on the top there's no safe way to access individual cells.

I think your friend should look in to why the batteries only lasted 4-5 years. Chronic under-charging and/or excessive power use would be chief suspects.