Originally Posted by DirtyHarry
Please explain the advantage of using 4-6V over 2-12V house batteries, I'm considering going with AGM. I currently have 2-12V.
The reasoning largely applies to FLA...
Most 12V FLA even those called "dual purpose" or marine/RV are not true deep cycle. 8Ds are generally the same design unless you buy specialty 8Ds with AH specs.
When switching to AGMs the FLA guidelines go out yhe window as they don't transfer directly. Batty mfgrs pack AGM into the same dimension case as FLAs but the FLA design advantages of plate thicknesses and depth of electrolyte below plates don't apply.
Battys are an energy storage device and there is no magic that allows you to get "twice as much" energy when you store it as 12V vs 6V... you need to consider the V as well as the AH and when you do the differences are very small.
2 - 6V AGM battys (series) are roughly 200AH @ 12V
2 - 12V AGM battys (parallel) are roughly 200AH @ 12V
Either of the above are roughly equivalent to an 8D +/-
Most AGMs list both AH & CCA
Both of the above will serve as deep cycle or start application equally well (confirmed by both Trojan & East Penn)