We are having an issue where the thermal breaker for the accessory battery is throwing itself from what appears to be the accessory battery not getting charged. As I have had it explained to me, when the battery gets low, the accesories are causing the battery to send more AMPs, and causing the thermal breaker to heat up and throw. This is a real problem at night when you have to wait for the thermal breaker to cool off and have no Nav lights.

When I had a mechanic look at the boat, he said the accessory battery was very low, but his tester stated the battery was still good.

Since we almost NEVER have the boat running accessories without the engine running, I am at a loss of why the accessory battery isnt getting charged much.

We have the switch set to 1. With this configuration, the alternator will never charge both at once, correct? It will only charge the starting battery, then charge the accessory battery when the voltage on the starting battery is high enough. Is this correct? If not, how does this work?

How would you go about troubleshooting the accessory battery not getting charged?