I'm using the CRC 5200 50c pack. Honestly haven't been able to run it enough on a high traction surface to put it to any serious test, but it seems peppy.
I did have to sand a bevel in the case at each side to get it to sit flat and solid in the battery pocket though. Front to rear fitment was no problem, but side to side the pocket was too tight to get the battery all the way flat. On the plus side, after hand-fitting it, the battery doesn't budge a micron once taped.