[SpEEdyBL]

50% charged for lipos is around 3.8 volts per cell at rest. The good thing about my hyperion charger is that it tells you what percent charged your pack is based on its voltage. But even if you were only able to use 50% of the pack the first 15 minutes, you will likely need more the second half, as the voltage is lower and you will need more throttle to get the current up and get the power you need.