Josh, I must bow to your friend's advice, as I have no personal experience with the typhoon.
If it really draws 20 amps, then you do need the phoenix 25. But that seems really strange, because I DO know there are a lot of typhoon shockies out there flyng with small batteries.
I suggest going to rcgroups and searching on the typhoon motor, and maybe posting a question for the lightest setup on a shocky with the typhoon.
www.rcgroups.com