I have a similar set up on my 420 sedan bridge. The battery charger monitors the voltage and if it needs a charge, it applies one. If not, it goes into float mode, which periodically checks for voltage drops. In other words, it won't overcharge your ...
Check the raw water intake for leaks. Also, you may want to check your freshwater tank/hoses. Also, check all your engine coolant hoses for leaking attachments - typically a loose hose clamp. I'd make this a priority project.
