That depends on your application. That motor can run at a variety of powers up to 50kw, so let's pick some numbers to make a simple example. If you want to average 24kw for an hour you will use 24kwh (kilowatt hours). The batteries you mention are 3.2v and 15ah. 3.2v * 15ah = 48wh, so ~500 of them will get you 24kwh. The motor's only about 90% efficient, and you don't want to run the batteries from 100% to 0%, so add some margin for that.
This forum doesn't have a large number of DIY builders, so this kind of technical question may get better responses at endless-sphere.com. A lot of very experienced ebike and motorcycle builders hang out there (including a few that have used the AC20). Just lurking and reading a pile of threads there would probably be useful to you. You may well find that you don't need 24kwh of batteries to achieve your goals