Re: Battery Sizing - am I crazy?
I agree with what's been said and your plan. If you're not going to do any rewiring then you want both the batteries to be the same type and age so that you charge them in parallel. It appears that someone wanted to have the battery bank be a larger capacity than needed for engine starting and light loading. The current, and more practical, thought to address this is to have a bigger deep cycle type battery for the hotel loads and a smaller starting battery that's spec'd to your engine requirements. with this type of arrangement however you'll need a different battery distribution panel which one battery is for the engine and the other for hotel loads, with a cross connect feature. You'll also need a charging circuit that uses a VSR relay or duo type charge that allows for the fact that the different batteries charge at differrent times and rates.