Here's the Fullriver AGM battery I recommended:
http://www.fullriverdcbattery.com/battery/DC115-12Notice that it has 115 amp hours of capacity ... which is very good capacity for a Group 31 AGM battery. It also weighs in at about 72 lbs. and many folks think that means there's a lot of lead in the battery -> which they consider as indicating good construction. The recommended float voltage (the voltage to be kept on them while the RV is in storage and also OK to be kept on them all the time when camping with hookups) for this AGM battery is 13.6 to 13.8 volts, which is exactly the output range of the standard converter in many RVs. This battery can also be charged up using this same voltage from the same converter - it just takes longer than a charger with a higher boost-voltage range - but not as long as a regular wet cell battery would take because AGM batteries charge faster at all voltages due to their lower internal resistance.
This battery is not an inexpensive AGM battery - but it's not the most pricey, either.
