- - Do not forget to install a ANL bus fuse up close and personal to every battery's positive terminal. This is now a ABYC requirement and even beyond that I have seen a half dozen boats over the years burn to the waterline due to a dead short allowing max battery current
to cause the battery cables
to catch on fire. Every battery "bank" needs to have the bus fuse between the positive terminal and the battery cable running to your loads or battery switches.
- - If you are going to install a separate/dedicated engine starting battery then to install an "emergency" cross-over switch you need simply another cheap
battery switch with only 1/2/off. Should your dedicated engine starting battery go dead or short out you want to be able to disconnect it from the engine starter and then connect the alternate (house battery) to the starter. Never parallel a dead battery with a good battery.
- - Specifically you connect the "common" terminal of the battery switch to the engine starter and then a battery cable from the #1 battery switch terminal to starting battery. The #2 terminal on the battery switch is connected to house bank batteries - ideally to the "common" terminal of the house banks battery switch which will allow you to choose which house bank battery you want to use to start the engine.
- - Without a dedicated starting battery your original diagram is fine - just add the battery ANL bus fuses
and a "battery combiner" between the two battery banks.