[C320-list] Starting Battery Question

[crashley at gte.net]

I've read a lot about adding a third, smaller starting battery and combining the two existing 4D's into a single large house battery. This sounds attractive and I may want to do this someday, but I have a basic question. If you use the existing battery combiner switch it will parallel the 4Ds and the new smaller starting battery (in the "all" position) for charging from the alternator but I thought I've read that you never want to parallel different size and/or aged batteries. How do you get around this? Is there any way to avoid paralleling the house and starting batteries and charge both batteries from the alternator? The shore charger is easy to configure since it has two separate outputs already. Any advice?

CRA
Rosebud #882