What happens if......(battery question)

[72BUG]

I connect a heavy duty starter battery to my leisure battery?

I have a large 110 a/h starter battery which I'm not using. (I originally thought it was a leisure battery as it came out of our old caravan) I was thinking of connecting it to my 110 a/h leisure battery to double my battery life. Will this work or will the starter battery simply suck the life out of the leisure battery?

[a1winchester]

Hi! Martin,

It's usual practice to only put very similar batteries together in parallel, and even then it seems you would need a heavy duty diode on one of the circuits to prevent one battery trying to charge (or discharge) the other. Other recommendations are to put fast blow fuses on both batteries.

The worst case scenario is for one battery to drop a cell, which causes the other to go down too, and you then have to replace BOTH batteries.

Even slight differences beween producers and types, like different lead alloys, cause slightly different topload voltages, temperature dependencies, etc.

Your batteries are so different that it's probably a non-starter (no pun intended!)

Would be interested in others' opinions.

[kevtherev]

Charge them both up and connect them in parallel...

[jamesc76]

To connect um together they both have to be exactly the same amp age etc etc, you will wreck one or both of the battery's if you connect um!

[ghost123uk]

I have a small motorcycle battery that I use for starting model aircraft engines on the flying field.

It is permanently wired in parallel with my large auxiliary battery to keep it "topped up".
Been like that for at least 3 years and both batteries are healthy.

Not that I am saying anyone is wrong here, the "common knowledge" is that it not recommended, but it seems to work in my case

[Oldiebut goodie]

Charge them both up and connect them in parallel...

That's what everyone else does with no ill effects.
My boat ran like that with the same pair of mismatched batteries for ten years.Neither of them were wrecked.