hey guys i think i know but want to make sure.im putting in a second battery on boat does my negative cable from the second battery go's to the neg. post off the first batt.then the neg.post off the first to the engine.is this correct
but only do that if both batteries are identical.
If one is bigger, or one is a deep cycle then keep them isolated.
just have one back up battery, or a battery for accessories.
the way you have it, it will be one big battery, not 2.
so once it is dead, that is it.