So I need new batt... 1,2 or 3?

I considered doing the 2-6 volt batteries, but decided that with my space constraints, I didn't really have room for 2 batteries at this point. So I got an AGM battery, Optima 8052-161 (blue top). At the same time, I changed out my engine battery to AGM, Optima 8025-160 (red top). I have been extremely happy with this setup. I can spend 4 days running the water pump, lights, mp3 player, and charging cell phone, laptop, etc. without concern. At the end of the 4 days, I still have a full charge on my house battery. I do use a battery puck light for my late night reading, but only because it's not as bright as the overhead light. I also do not have solar or a generator, so my battery is all I've got.

If at a later date I decide I need power longer, I will use 2 of the Optimas in parallel.

My decision was made in part by this link: http://www.marxrv.com/12volt/12volt.htm