I bought a Turnigy Nano-Tech 2650 35-70C
for $30 and looks like it will fit fine. Unfortunately, I decided to by an 89" Slick instead of this plane so I don't need this battery and it is currently out of stock. If anyone is interested in buying it, PM me. It has never been out of the box other than to measure it.
From physical measurements (ie, actual not from specs):
L = 136mm
W = 43.4mm
H = 22mm