2 cell lipo = 8.4v fully charged
your average receiver and servo wont last too long at that voltage .
Many nitro guys ( who need a battery for the receiver ) have gone to high voltage servos and receives for use with lipo batteries .
Cheap ESCs often have a 5v bec ( battery eliminator cicuit ) , better ESCs have an adjustable one , so you can always have 6v if you want