Batteries and their Capacity to CHARGE to full.

easy way to get around this is hook the charger on one batt, and then the other, but you will have to be handy to make the switch. You cannot put 2 disimilar batts in parrallel. But yes to confirm, different batts will do either one of 2 things, 1. as you described, or 2. overcharge and kill the small capacity batt.

From my understanding Al that is the theory but in practice it often doesn't matter. Ideally batteries wired in parallel should be of the same size, age & construction to maximise the ability to reach 100% charge & increase life.
Mixing batteries may mean one will only ever get to 95% charge & die 6 months earlier. Will it still work? Yes.
Cheers Craig........

Assuming that two batteries are of the same construction (lead acid), if both batteries are connected in parallel and one battery supposedly gains full charge before the other, the charger will continue to punch taking the path of least resistance to the lower charged battery. The fully charged battery is in danger of being over charged, but batteries hooked up in this manner equalise their charge states and the charge surfs to the lesser charged unit. So the charger doesn't see two seperate batteries, but one big one.

Al,
Can I suggest he was incorrect ?

Reason being;
When the two batteries mentioned are charged when using an "automatic battery charger" which I believe would be a 240v battery charger, therefore the vehicle is stationary, or you have a dam long cable :-)

In the above scenario, (240v battery charger) the two batteries are NOT connected in parallel under NORMAL conditions.
Reason being there is a "battery isolator" separating the Cranking battery from the House battery, when the vehicle engine is NOT running.

Therefore simply charge the *House* battery first and when it's fully charged, disconnect the 240v charger and charge the *Cranking* battery second !

Mainey . . .

Thanks members for the prompt and helpful replies. They confirm what I believe I am experiencing at the moment and so with your information I'll solve it.
regards,
Al.