What I’ve done, is to install a two battery, battery switch with an off and both battery position.
That way regardless of what I’m doing, I can switch to what’s required.
If I happen to drain one of the batteries; I can switch to the other or have both batteries on line to get me out of trouble. Also while I’m powered up I can charge both batteries.
I did have a small issue with the fish finder and VHF radio; while using the trolling motor; but a few automotive style capacitors (condenser) seemed to cure the problem.
I connected the capacitors across the power feed and ground of the finder& radio and a third at the trolling motor. The capacitors are cheap and can be had at any automotive supplier. As long as the kid behind the counter, knows what a condenser is; yes I’m talking old school, points & condenser. LOL
Another good thing about the battery switch is that you can shut all power off, when leaving the boat.
The only bad thing is that you should never switch batteries with the main engine running. There’s a chance of a power surge from the charging system; that could hurt the electronics’. There are isolators for the charging system but I never worried about it; I’m almost always the one at the controls.
Dan.