Battery isolator question
This is actually about my boat, which I suppose can be called a Recreational Vehicle.
I'm installing a second battery for non-essential accessories like the radios.
The ignition, starter, gauges, lights, and other stuff for navigation will remain on the main battery. I've also purchased a cheap little battery isolator made in China. The idea is to have both batteries charging when underway but, when the engine is not running, to be able to exhaust the 2nd battery without drawing current from the engine battery.
My understanding is that the accessories will draw from both batteries until the main battery falls below 12.8 volts, when it will disconnect. When the voltage on either battery exceeds 13.3 volts, it will re-connect.
My question is about where to connect a battery charger when needed. It seems to me that it should be connected to the engine battery. After that voltage exceeds 12.8v, the both batteries can continue to charge together. Isn't that what happens when the alternator is running?
But, the instructions for the isolator say to connect the charger to the 2nd battery. I'm not sure why. Maybe it will work equally well in either configuration, but I think I prefer having main battery topped off first.
Who is right? Me or the people in China?
2017 Thor Freedom Elite 23H