A battery that would fit without a need for larger back cover is the one I'm looking for. There is Innocell 1750mAh @ seido's for HTC Hero. Are there any batteries that hold more power yet still are same size as OEM?
Also, since I do ~10hr-drive trips every other month, I'm considering Seidio's or Mugen's ~3500mAh monster for those occasions. Always-on GPS + nonstop music playing + push email turned on all the way through + occasionally wifi tether for light web browsing is quite demanding on the phone. My old phone (TP) couldn't handle all that and would refuse to charge due to overheating :P
Bielinsk: that 2,000 mAh battery you mentioned fits in or requires a larger back cover in Evo?