by Conrad & Judy Kreuter
If you have a dual battery system in your boat, you may have noticed that only the battery selected by the battery switch is being charged while the engine is running. Turning the battery switch to “both” connects the two batteries together. This could be a problem if one of the batteries is low or completely dead, as the dead battery will draw a charge from the charged battery and may drain the charged battery so that the motor cannot be started. To make sure that both batteries are fully charged, install a low cost battery isolator.
A battery isolator allows each battery in the boat to receive a full charge even if it is not the battery being selected by the battery switch. This means you will never be suprized with a dead battery.
To select the proper battery isolator, check with your local dealer so that he can advise you of the proper model for your application.
Mount the battery isolator, which is about half the size of a normal battery, in a dry area somewhat close to the battery bank. Attach the battery isolator to an inside wall of the boat with self-tapping screws, or if you can reach behind the panel, you can thru bolt the unit. Connect two 10 gauge wires from the battery isolator to each positive battery terminal.
If you have an outboard, the alternator wire must be removed from the positive battery connection at the motor end. Check your motor’s wiring diagram to do this properly. Run a new 10-gauge wire from the alternator output wire of the engine to the battery isolator input terminal. Consult you engine wiring diagram for the proper connections if you have an I/O or inboard engine.