http://www.svrbatteries.com/audio_line.html
SVR Audio Series batteries. Simply incredible performance, I couldn't kill mine when I *did* try to. The SVR 31-12 will drop straight into a Gen4, dunno about the other gens. It says it's only 500CCA, but then again CCA is just about as accurate as the wattage is on an amp. Anyway, they're cheaper than Optimas, and they perform 10x better imho. I couldn't ask for a better battery. All the car audio fanatics in my area have been swearing by this battery for some time now.
EDIT: MSRP on this bad boy is only $95. You can't beat that with stick!