My M/H is a 1978 Ford Frontier 351 windsor 21,5 ft. It never came with a charger built in that charges from shore power. It only charges when the motor is running, from the alternator. There is a little black type cannister next to each battery on the inside of each fender,which I presume are isolators. Why I want a good charger for my new setup is because I remove my batteries each season,reason being I store the M/H a few miles from my home and I don't want them stolen and I want a charger I can trust not to fry them. I don't really want to go to the expence of wiring one into the system,I would prefer a portable type. I live in southern Alberta and it gets darn cold here, another reason I take them out. Thanks again. Glennis.