Originally Posted by Santa_Claus
I have now done several rounds of depleting, charging then equalization. Specific gravity shows that the front two batteries (easiest to maintain) are good, the back ones are near dead and plumb dead! I've heard that you should always replace all 4 at once, but does that make real sense, or is it a myth, like storing batteries on a concrete floor? If the front two are taking a full charge how can they drag down two new ones? TIA
Because they are connected together, current will flow from the batteries that have a higher voltage, to the ones that have a lower voltage......in effect "dragging down" the good ones.
In the ideal scenario, yes all batteries connected together should match in brand, capacity, and age.
Specific gravity readings are good, but no substitute for an actual "load test". Have the 2 good ones "load tested". If they pass that test also, then buying 2 more batteries just like them would seem a pragmatic thing to do.
If they fail the load test.....then buy all 4 new.