We use a setup that follows what the batteries were designed for. We use 6- T105s(deep cycle) for the house bank, and then a car start battery for the engine starting-both the prime engine and the genset. As was explained to me, the thinner plates of the starting battery provide the bigger (but short term) energy for the engine starter, but are not designed for the long-term use of a deep cycle. Both are isolated from the other. the engine alternator recharges then house bank, and the start battery is recharged via the genset alternator and a Balmar Duo-Charge from the house bank. I do, also, have a parallel switch so I could connect the 2 banks if I ever needed to....have never used it! The system has worked perfectly now for10+ years, thru Asia, the Medd, and now the Caribb.