Join Date: Jul 2007
Location: Windy Wyoming
Thanked 39 Times in 38 Posts
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Conventional wisdom sez batteries are like draft horses -- the team works only as hard as the weakest (or laziest) horse. So CW sez never mix new batteries with old, because the old ones will drag the whole bank down. New batts will tire themselves trying to bring old ones up to snuff.
OTOH, IF you are sure those old batts really are good, and the new ones are same size and type, then more battery capacity is always better than less. Equalize as often as possible, especially if you have 3 or more parallel strings. Once a week is not too often. Luck!