I just replaced my 3 batteries......I use one called "Big Mamma".....group 27 cost $85 and has 180 reserve amps.......(some guy on here said the reserve amps are the most important number to look at.....the higher the better)........been using them for about 14 years.........my battery guy told me not to go with the group 31 as they take forever to charge up......here is an excellent link for info on batteries.....

Deep Cycle Battery FAQ