Mario & Idie -
Mike Laupp did a great job of adding a second battery in his 2720SL, tying them down, and handling the weak-floor problem. See his thread at
http://www.trailmanorowners.com/foru...ead.php?t=1696
Ray is right - a pair of 6-volt golf cart batteries in series performs a bit better (it is not a dramatic difference, though) than a pair of equal-size 12-volt batteries in parallel. On the other hand, you already have a 12-volt battery that you may not be anxious to trash, so cost may enter the equation, too. I will probably make the switch when the original 12-volt battery dies.
Bill