40 hp motor is huge for that application.   That would be a
peak (5 minute rating), which is still about 100 pound motor,
needing 400 Amps @ 72V....  even with high efficiency batteries,
about 80 pounds (minimum).  Catch with AGM batteries is they hate
going to full depletion mode, as the 1000 cycles will drop into
the 10's of cycles... meaning 160 pounds of batteries. I wonder
what battery it is using? LI-Ion most likely.

So figure out what an extra 180 to 240 pounds of dead weight does to your performance!

I used to follow the Electric Vehicle programs very closely with
the old job, but haven't been active with it in 8 years. Lots of
progress with batteries, but like my Sister who bought a hybrid...
but commutes on the freeway I told her to buy a smaller 4 cyl
vehicle to save gas (you have to drag around an extra 300 pounds).
My '82 Datsun 210 still gets 47mpg.

Old vehicle (long since history):
http://www.evalbum.com/121f.html

Tom