With any three wheel design needs to control the Cg:
(click on image to see source article)
If you can get consumption down to about 100Wh/mile, then you'll need a 11-12kWh pack (with about 10kWh DOD) and based on the cells I was planning CarBEN EV5 around, that would be a volume of about 3.5' x 10.5" x 5.5". The individual cells are 10.5" x 5.5" x 0.375" and you would need about 112 of them. (CarBEN EV5 has space for ~768 cells for a ~55kWh pack.)