GC2 series pairs capacity

[camperguy99]

I've read a lot here about not mixing batteries, new with old, different brands, etc. Folks state that a bad battery will destroy the good one(s) paired with it? Can some of you tell me why this is so? I have 3 series pairs of GC2's for a total of 680 amp hours and don't seem to be getting anything near that amp hours capacity? My Magnum 100 amp charger will put 105 amps out and I have measured almost equal charge/discharge current in each of the 3 series pairs. Seem OK to me but don't like the results?

[TyCreek]

You'll get the total capacity of about 3x the weakest parallel pair. If all 6 batteries are 100% then you'll get closer to the assumed or rated capacity. It only takes one to slowly destroy the rest and speed up the death of the weakest.