Originally Posted by AlanF
I think the one-big-bank vs. switching-between-banks will be a never-ending debate, and one that I don't think is a slam-dunk. I've gotten incredible life out of batteries in separate banks (O.K., they *were* Surrettes), and that was flipping the old A-B switch back and forth every day or so. The argument for separate sets is that they will always charge at their natural rate, unaffected by the possibly sulfated/hot/cold/whatever other battery in their bank. I think when they're new, having them in parallel (one large bank) is fine, but as they age, it tends to give grief. (A good argument for sets of 2v cells that are always in serial!).
Then again, I wouldn't argue with the large-bank proponents, either.
My other two cents - I think the Sterling B2B is a really cool idea, just haven't gotten a chance to put one in yet. Hoping to hear some first-hand comments.
Just remember that there are two main advantages to the single large bank:
1) A single large bank means each battery sees a lighter load. Ah's are specified at certain load current (the 20 hour rate) - anything more and you get less Ah's, anything less you get more. So for any given load when you add batteries you always get 'extra' capacity as the load for each battery goes down and therefore it's effective capacity at the new lower discharge rate goes up. It's like 4 lightly loaded horses pulling a kart will take it more than twice as far as 2 heavily strained ones.
2) You're discharging each bank less. Discharging a single large bank to 20% every day is a lot better than discharging a half bank to 40% every other day because battery lifetime goes up exponentially as discharge depth goes down.
Note that 1) also helps with 2) because the 'extra' capacity further reduces the depth of discharge for a larger bank.