Paranemertes:
Wow, thanks for all the replies! You are probably right about the 300 amps, I just want to be safe. I want some decent range so at least 100 amp hour deep cycle lead acid batteries. What about a diagram?? I'll try and make up one that I think would work. Thanks again!
Are you sure that is a realistic size/weight budget? Have you ever tried picking up a 100 AH 12V lead acid battery? They are big old things.
If you're planning to be up around 72V you need six of them. How do you physically fit them in/on the bike? Is the frame strong enough to carry all that weight, and can you actually ride a bike that heavy? Also remember that lead/acid won't like being tipped over, I guess with a bike that weighs more than you do this might be a risk.