I am not disputing that. What it cares about is that it is isolated and gets charged up to it's max charge at EXACTLY the right voltage. You can't charge them together in parallel like your boat setup. It will degrade the battery over time and that high dollar battery that should live 10+ years will live 2-3. An AGM battery and a wet battery are not the same. You can treat them the same but you'll pay for it in getting wet battery performance from an AGM.

Here's a link to a PT thread I got going about the same time. It's starting to become clearer, though not completely, so anyone with expertise in this area could certainly help us.



https://www.pro-touring.com/threads/...Battery-system

Have you looked how they do it in diesel trucks. And or check an RV shop as well.

Haven't had the time recently. Hopefully we'll get some experts to chime in who have studied this.

I didn't think people still used wet batteries. :headscratch:
maybe in some correct restoration build. I always used the Odyssey PC 1200 in the wakeboard boats, I had 3 in mine.

I appreciate you trying to help. The point of my question has been lost I think. The take away here I suppose is that a regular alt will only get the AGM batteries to about 80% of their proper charge. It takes a 3 step charger to get them topped off. They will work fine for years like that but they won't have the same efficiency or life than if they were properly charged. That's all well documented and easy enough to find.

The thing I was looking for is the same thing the RVs do with the BCDC charger but to also be able to automatically use the house battery cranking if required. It appears that a BCDC charger or advanced regulator set up for dual AGM batteries AND a standard parallel switch to use in the event of an emergency is the best way to handle it. I'm sure there is some super high dollar battery management system that will do it automatically but the BCDC charger and switch are already going to be well over $500