Starter or House Battery?
On my boat, my theory was to ensure that no bone headed mistake would ever allow me to accidentally discharge the starter battery. With that in mind, nothing but the starter has the ability to suck amps from the engine battery, and the only other wire touching it is the lead from the battery combiner for charging from the alternator or shorepower. If the starter battery does somehow let me down, it''s lead is lead through a switch that lets me start using the house bank. I can go sailing for weeks and never touch the battery switches, and not worry about whether I''ve accidentally let the starter battery discharge.
Whatever setup works to get you confident that you''ll at least get starter sounds when you press the go-home button, is the one to install.