Electrics have shorter run times because when a battery pack is dead, you have to stop and wait around for it to recharge.
As for nitro, you could run it for days, you can just top off the tank when it gets low.
Part of this is correct, however the other part is incorrect.
A good battery will get much longer run times, charging a battery is the equivelant of re-filling the tank. After all a combustion engine can only go so long, you re-filling is like re-charging the battery. A nice battery will run for hours on hand (12,000 mAh li-po).