12 V to 12v deep cycle?

What would happen if I hooked up a 100ah car battery to a 101ah deep cycle battery (in parallel)?

Why would you want to…?



Nothing funny would happen. They would charge and discharge together. If one was older and not holding a charge as good as the other one it would suck the good one down to its level.

You’d get a sort of hybrid of the two (if in parallel), where you have a bit more capacity and a bit more peak output.

It’s important to understand that the construction of the two internally is rather different. Starting batteries are focused on surface area of the lead plates to deliver peak energy outputs, while deep cycle batteries focus on thicker plates to support and withstand deeper discharges. Real starting batteries never want to be deeply discharged and just a few deep discharges can ruin them.

If they are not at the same voltage then you will have some current between the two until the voltages are equal.

You could also add a riding lawn mower battery or a motorcycle battery to the mix.

You could put a Hell of a lot of them in parallel and see if they’ll pop a 5000A fuse.

What will happen after they self-balance voltage, will depend on what you do with them.

Thanks all; I just replaced my car battery because it was old and not holding a charge; I keep the marine battery hooked up to a solar panel jic. Then I wondered—————now I know; it ain’t gonna happen. :student:

5000 amp fuse: