Battery isolators- dual batteries
I see a couple different styles of battery isolators. One is an electronic kit with 3 lugs where the batteries charge automatically but they advertise they have a 0.5 to 0.7 volt power loss.
Another is like an old Ford starter solenoid with contacts and stuff.
A third is a key switch where you can set it to one or the other battery individually , both or off. I'm not sure how you would charge this one automatically though unless you manually switched from one battery to the other while you are on a trip?
What do you all use? I bought a used 2006 Prowler 650 H1 and it has a stereo and 4 huge HID lights on top. They guy installed a second battery but only installed a On-Off type battery isolator switch so it could switch from one to the other but not both or completely off and the batteries were draining down in a day or two unless I keep it on a charger. I disconnected the second battery and switch and now everything is holding a charge for a week now so something was wired wrong.