Supervee25, were you referring to using two 7.2v packs or just one? Cuz the sv27 is built for two 7.2v cell packs, not one.

If you're referring to one then like what twomanytoys said the thing will probably haul at about 20mph, maybe even less.
A 7.2v pack in a SV27 would be the time to call in for a high amp SAW setup lol.