Re: New Batteries
With a 3 battery, 2 engine setup you need 2 Marine Starting batteries for the engines and 1 Marine Deep Cycle battery for the electronics. As far as *what* battery type/brand you go with, well everybody has an opinion on this. Some people think its worth it to go with AGM style batteries and others are happy with *standard* Marine batteries. AGMs are definitely better, but whether they're worth it to you or not is a different matter.
Personally, I've had very good service with the standard marine batteries from Walmart. If you want to go AGM type, Sears has a good one. Whatever you get, make sure the starting batteries are at least as big as recommended by your engine mfgr. The house battery size is not so cut and dried, but I think its a good idea to go with as big a battery as practical - a group 27 at least.
Ken