Probibly past the "beginners" forum area, really.

There are a lot of options. You can hook up the batteries with a Y like that for discharge, but don't even think of charging them that way, you'll have to unhook and charge seperately, and make darn sure you get them both fully charged before hooking them together. You'll get some folks telling you that you can't do it at all, but I saw some test data recently that showed that cross charging was minimal.

Now, the big question is WHY do what you are doing. If you want more battery capacity, you'll do better with just a single bigger pack. Get somethign in the 1800-200+ range and a field charger. The guys who run redundant batteries do it for safety, and they are going to have rudundant switches and all kinds of things to try to eliminate a single point of failure, but as I said, that's way past this forum.

Try asking over on the forums for acrobatics/IMAC and you'll get a lot of answers if you want a redundant system