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The protection of electronics is an additional feature. The system itself monitors and isolates each battery for charging based on need. Similar to you running in the "all" position with your current set up but a bad battery would not be draining the good battery. You can also isolate your functions accordingly. You can run the functions of your boat off of one battery with a fully charged battery available to "jump start" your boat by turning the switch for a moment to "combine", then back to the original positioning. You could protect your GPS, fish finder, CB, VHF, etc... incidental of how much they cost you. Lights and other accessories are not bothered by the spike/transient that shoots through your system when starting.
Garris