An RV/Marine battery
is a compromise between the two. It is suitable for either application but not the best choice for either.
A 6 volt and a 12 volt RV battery
contain about the same amount of lead/number of plates. They just differ in the number of plates per cell. Two 6 volt batteries are approximately equal in price, amount of lead/number of plates, purchase price and amp/hours as two 12 volt batteries and will last about the same time before they need to be recharged.
The 6 volt batteries will be wired in series. The 12 volt batteries will be wired parallel.
I use 2 12 volt batteries, one at a time. If something gets left on and drains the battery
, I have a full one left.
I use 120 watts of solar power
. This keeps my batteries full for months. No other charging necessary.
AGM batteries don't require water, don't spill if tipped and are more vibration resistant but you pay a premium for these features