Connecting batteries in parallel.

[Troubadour]

However if I were to leave them connected and not charge them the 'see saw' effect kicks in and in a week or so I would have flat batteries.

I'm glad nobody has told my batteries that and consequently it doesn't happen even after a couple of months.

Seriously it isn't a problem provided both batteries are healthy. If one gets an internal short it will drain the other.

Many military and commercial aircraft use sealed lead acid batteries in parallel and that isn't a field where you take chances.

[claudio]

I'm glad nobody has told my batteries that and consequently it doesn't happen even after a couple of months.

Seriously it isn't a problem provided both batteries are healthy. If one gets an internal short it will drain the other.

Many military and commercial aircraft use sealed lead acid batteries in parallel and that isn't a field where you take chances.

I've left mine fully charged, 6 off 220AH in parallel for over 3 months without trickle charge and without problems.

[Chris_Robb]

I'm glad nobody has told my batteries that and consequently it doesn't happen even after a couple of months.

Seriously it isn't a problem provided both batteries are healthy. If one gets an internal short it will drain the other.

Many military and commercial aircraft use sealed lead acid batteries in parallel and that isn't a field where you take chances.

Having 2 100AH in parallel rather than 1 200AH (which in theory is better), gives you a safety margin if one fails; just isolate it. At least you have something left.

[sarabande]

However if I were to leave them connected and not charge them the 'see saw' effect kicks in and in a week or so I would have flat batteries.

That's in theory, but somehow it's not how it works in practice....

[ghostlymoron]

Having 2 100AH in parallel rather than 1 200AH (which in theory is better), gives you a safety margin if one fails; just isolate it. At least you have something left.

And also won't give you a slipped disc when you lift it out. I'd go for 3 x 75aH just for manual handling reasons.