Lots of options. Depends how good you want it and how much you want to spend. Take a look at my thread:
https://endless-sphere.com/forums/viewt ... 10&t=85758
This is a 14s 55ah pack.....
It would fit inside an xu case with room to spare.
It would be about the best you could get for the xu. at the other end of the spectrum you could use RC cells such as Turnigy.
Good power density but if you want this to be a serious bike then you need good thermal management on Turnigies because they get cranky if too hot.