Thin 52v battery?

[rocwandrer]

I commissioned a custom frame specifically to build with a bbshd. It is an elevated chainstay fat bike setup so the chain line works with the width of the 100mm bbshd. But the space for the battery was supposed to be 5" to clear the battery I have and it came out just under 4". Anybody know of a compatible battery that will fit between two parallel tubes 3.9" apart?

 

[Mongo]

I think the Hailong / Reention tray-style cases are approx 3.5-3.8 inches wide, and the smaller capacity ones are the same height. em3ev's hard case triangle bag is slightly narrower, IIRC.