I took the measurements (14.5”L x 3.75”W) from the page on the shop here for the 52v slim shark buttery pack and made myself a cardboard cutout. The battery pack does not appear to be a perfectly square cornered box, and has some angles on both long ends.

if I can get this battery pack closer to the neck I think it will clear the rear shock. I want to find before I spend $500 on this battery though.