Wiring Suggestions for the Master Battery Switch and Multiple Battery Banks

I have never been happy with the way that my own boat’s battery switch is wired and went looking for ideas and suggestions on alternate methods. I stumbled across a couple of interesting Ideas and I thought that I’d share them here. These methods may not be new to some of us but both are somewhat different from the way that most boats are wired at the factory. Here they are.

Battery Switch Metod 1

The above shows Method #1. The 1-2-Both battery switch is at the top center and for clarity I have just shown the 1,2 and Common terminals. Wiring your switch in this manner has the following advantages:

You would likely run with the battery switch in position 1(connecting the house bank to the common terminal on the switch) for most situations. The house bank is shown as two 6 volt batteries wired in series but the configuration doesn’t matter. 

1-With the alternator wired directly to the house battery bank it allows the house batteries to be charged separately from the reserve (or starting battery). If it ever became necessary to charge the reserve battery off of the engine the switch could be moved to position 2 which combines both battery banks and the common terminal.

2-While at the dock the shore power charger would automatically charge both banks regardless of the battery switch position.

3-The shore power charger will keep the reserve battery fully charged and maintained eliminating the need (in most situations) to utilize the engine alternator.

The only option that this configuration doesn’t cover is that it won’t completely isolate the house bank from the rest of the system but if you feel that its necessary adding a switch to the negative side of the house batteries will accomplish this.

Method#2

This is similar to Method #1 except that the engine starter is switched and connected to the reserve battery only. This allows the high engine starting loads of the starter to be isolated from on board electronics which some feel that is a good idea. Hide the starter switch and it becomes an effective anti-theft devise.

Batt Sw