The 2nd battery and one of these is a fool proof no BS setup. Extremely simple to understand by "Anyone" that gets on your boat. No having to remember to switch to this battery or that battery part way thru the day. I do NOT condone running a standard battery switch in "Both". A shorted cell in one battery will kill Both batteries if the switch is in "Both". That is a combine position to be used in a emergency only and then switched back to #1 or #2 after the motor is started.
BEP
http://www.bepmarine.com/Dual-Batter...-180-1464.html
