I like that knife sheath idea.

I suppose the best set up would be 2 batteries.......one for engine, one for all accessories.
Set up on on/off switch so both batteries can be
1. charged by outboard
2. can switch to " both " in case starting battery is weakened.
Accessory battery located up front, inside cuddy for weight distribution.

That said, my V21 is one battery, no on/off switch and all good.
Just don't leave switches on as posters have said !