new and "slightly new" batteries. To mix or not to mix?

[ScotchPine]

I've certainly heard that it's best to avoid mixing used batteries with new. Unfortunately when I bought the eight 6V GC batteries, 4 were taken by workers to be lightly used over the last 6 months at the little camp, the others stayed put in the basement waiting to be used. The 4 being used were brought back and all were moved to a new spot. There's little I can do to tell which is which at this point. I don't want to throw out good batteries that have seen little in the way of discharge, nor do I wish to somehow ruin the unused. So in reality, just how bad is it to mix and match? Were I even able to discern used from unused, is it worth relegating them to the scrap heap? I have no other areas they can be used and I'd need to replace them with yet another 4 new batteries. Ah..what to do...

[MountainDon]

Sounds like they all celebrate the same birthday but have been used differently. The birthday is important as well as how well were the used ones used.  If it were me I'd place in service together and treat them all to a full charge, then an equalization charge. Take hydrometer readings and see if they all come up to be virtually the same. If they do all come up to the proper sp gr than they will all likely function well as a group. Depending on how those used ones were treated while being used there may end up being little difference between them.

[OlJarhead]

Sounds like sound advice for me too (thanks Don)....I have a chance to buy 4 used GCB's that are the same make and model as the ones I bought 2 and 3 years ago and am using now.  The ones I found are 1 to 3 years old but if I charged them all up and equalized them etc then I should have a good idea of where they are.

Incedentally, all 8 of my batteries have not shown any appreciable difference in SG testing previously and have never been equalized.  I have heard different ideas regaurding equalizing batteries but I think in this case it might be sound advice for me too.

[NM_Shooter]

Test them as Don indicated, then determine the weakest battery and use it as your benchmark for discharge use.  What I mean is to consider that all the batteries have a similar capacity as your weakest battery.

Consider how you will be banking them as well.  A dangerous condition can exist when one cell in a series bank fails. 

Measure them, keep an eye on them, and don't over-discharge.