I received the booster pack batteries from Doctorbass on the endless-sphere.com forums. However, I found out that these aren't enough to create a strong and equivalent booster pack for my 37V 13AH main Bosch Fat Packs. I would need another 6 or so packs bringing the total cost up to the mid $150 range. I've decided to bag that for now and switch to a 72V configuration with the rear 9C motor. This should give me the necessary range and speed to get me to and from work.