With just one 12V house battery in an easy-inspect roll-out tray, I think the cost for an AGM is not worth the expense. As well, I am not convinced that if you have two 12V house batteries, the cost for AGMs is worth it. To me, the AGMs are ideal when you can't easily check fluid levels like I now have with my current 6V conversion.
My experience with two 12Vs is that they drain out of sync with each other. One drains much faster than the other, then boil-overs happen when charging. With all that going wrong, your power reserves suffer, and battery life suffers too. I am no expert, but that has been my experience with two pairs of 12V batteries, and one pair of 6Vs.
I look at it this way. Every battery operated toy, flashlight, or other electronic devise using rechargeable or disposable batteries, the maker stacks the batteries (in series) like the two 6Vs are in my PC for "best energy utilization". With 6V AGMs, I surely don't have any boil-overs. I wonder if PC owners with wet acid 6V batteries deal with boil-overs.
Oh, I forgot about the cigarette lighter plug-in volt meter. I bought mine on Ebay for a couple dollars. They come in many different color read-outs. I bought green to match my dashboard color.
HERE is a blue/red for $1.83 with free shipping.
HERE is my green one for $5.35 with free shipping. Buy two, plug one in the dash up front, the other in your 12V socket to the right of your main TV and you're all set.
