I installed a single group 31
NSB-AGM31. These guys had the best price out there answered all my questions even though they were very busy and quick shipping
Northstar AGM31 Car Audio Battery Group 31. I don't know if I "had" to but I trimmed the tray so it could sit all the way in there without bulging the sides. I'm not a fabrication guy at all but took about 15-20min of air grinding taking my time to make it clean. I understand it is probably the most expensive one, but it's also the best one you can buy and it's made in the U.S.