I have a 26ah lead acid that was one of the lead acids I've used. I was more fond of the 18ah and, if I were to do it again, I'd buy two of those (if I were still using lead acid that is).
I'm with Mandobart on the pure sine inverter too but the word is that the modified domes work fine . Look to pure sine if you plan on using the battery often. I use a Powerbright Aps300. I recommend it. Can be bought at amazon $130.
These days I'm using lithium batteries and a fast charger. Most of it was described in detail on the recent thread
http://www.acousticguitarforum.com/f...d.php?t=427595