It doesn't take much of a battery to start a 30hp or less diesel
. Two golf cart batteries pack way more energy than is needed. The problem with only one battery bank is inadvertently letting the battery(ies) discharge, BTDT. Fortunately had a hand crankable diesel
so was able to get the engine started and charge the batteries back up.
FWIW, if you ever do find your self with weak batteries, sail downwind with transmission
in forward. The water
flowing over the prop greatly cuts down the energy needed to turn the engine over.