Well I'm running an extra Xstatic Batcap 800 in my hatch and I paid $100 for it since a friend of mine owns a local shop. From what I see, they run for about $150 online and I'd say they're worth it, given I dont have much experience with batteries. This one works well for me though. My stock alt is 100a and I still haven't done the "Big 3", and at one time I was running darn close to, if not, 2000wrms with stock front battery, zero gauge wiring, and the Batcap in the hatch and the lowest voltage drop I got was about 11.6v at idle and full tilt on super low notes. For daily driving, my voltage stayed perfectly fine.