Dual Battery System Setup

[Doug1]

Originally Posted by ilikeike

I put together a couple of multi battery wakeboard boat stereo systems. Keeping it simple I just used a starter solenoid.
Key on engine running solenoid closed all batteries connected and charging.
Key off or acc. Solenoid open, batteries isolated.

Simple and works, for years.

I would but my research led me to a few articles that point out that the AGM batteries require a DC-DC isolator to charge to 100%. Apparently they otherwise only charge to 80% with an basic switch. Same thing with 120v chargers. You should use one designed for AGM batteries verses wet batteries.

[ilikeike]

Originally Posted by Doug1

I would but my research led me to a few articles that point out that the AGM batteries require a DC-DC isolator to charge to 100%. Apparently they otherwise only charge to 80% with an basic switch. Same thing with 120v chargers. You should use one designed for AGM batteries verses wet batteries.

So the agm battery in my car doesn’t charge ?

[Doug1]

Originally Posted by ilikeike

So the agm battery in my car doesn’t charge ?

That is your statement not mine. The point being is that you cannot hook them up exactly as you did in your boat because they only get an 80% charge that way. Look it up.

The bottom line is you need better equipment to keep your AGM battery fully charged and to maximize it's life. The voltage regulation needs to be more precise than a wet battery.

I also imagine your cars starts fine with a semi fully charged AGM battery. It will just not live nearly as long as it should.

This stuff is not as simple as your are making it. Using the same old style charger a Lead acid wet batteries and also an AGM is like trying to run the same fuel pump for both carb to fuel injection. Can you get it to work? Yes. Will it last? No

Here's some info to help show that 12v isn't just 12v.

https://deepcyclebatterystore.com/ho...ain-batteries/

[ilikeike]

I think a car alternator charges the agm battery just fine, they wouldn’t use an agm in a automobiles all these years if it was an issue.

The battery doesn’t know if you pulled the cable off the post or simply opened and closed a disconnect switch.

[Doug1]

Originally Posted by ilikeike

I think a car alternator charges the agm battery just fine, they wouldn’t use an agm in a automobiles all these years if it was an issue.

The battery doesn’t know if you pulled the cable off the post or simply opened and closed a disconnect switch.

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.

[Doug1]

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

[Zspoiler]

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

[ilikeike]

Originally Posted by Doug1

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.

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

[Doug1]

Originally Posted by ilikeike

I didn't think people still used wet batteries.
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