What's your chargers voltage? 70v or so? divide that number by 4.2 to get equivilant RC lipo voltage.
If your controller can take it, ( 72v controller?) then 18s is a handy number for lipo. Three sets of 6s packs. 63v nominal, 75v full charged.
Figure that out of a 5 ah pack of lipo, only about 4.5 ah is really avaliable for use, so as to avoid accidental overdischarge. When they talk about 5 ah, they mean going to 3v, and you don't want to do that. Stop at about 3.65v per cell. As it ages, capacity will drop another .5 ah or so per pack.
THE LIPO RULES. NEVER ABOVE 4.3V NEVER BELOW 2.7V DON'T PUNCTURE
Ideal charging /discharging range for Lipo, 3.65v minimum 4.1v maximum
See battery technology section, FAQ thread at the top of the page for lipo noob info.