Join Date: Sep 2007
Location: Pasadena Md - Magothy side
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Nigel Calder does it best, here's a try (this can be like a religion, so it might get fractuous).
I use 1 bank, 315 ah, with a starter battery that is exactly the same (AGM deep) on a ACR, battery switch always on 'both', 80w solar the only charger I've need all year (and the occasional iron jenny adding in). I also have a solar booster and battery monitor keeping it all toasty.
Charging works fastest/best with stages, and most chargers use 3. Bulk rate is the fastest rate - and is usually based on percentage of charge (which is calculated by the voltage level, but that's too deep) -
If you have two batts that hold 100 ah each as 2 banks, and they are 50% full then when charging them at 20ah (average charger) they will bulk rate charge to the 80% level in 3 hours (10ah per battery, half the output of the charger) then go into the next stage of charging. At this point you have two banks, each with 80 ah in them, meaning a usable 30 ah each before you cycle the battery - and you have to watch them to make sure you don't cycle the battery.
Meanwhile, as one bank 200 ah, drained to 100ah, dumping the same 20ah via a charger; keeping in mind that 80% of 200 is still 160 you reach 80% in the same 3 hours - but now you have the use all the a total of 80 ah without having to worry about switching banks, cycling the battery.
Using an altenator, with larger ah output the single bank gets even better - you can really pour in ah much faster if the bucket is bigger to begin with.
The rate of fill stays pretty much the same for the next two stages of charge, it still works on percentage of overall all charge (read by voltage of the battery) - the bigger the bank, the more ah you can pour in before going to the next, slower charge stage.