A lot of the older servo components were never designed for voltages above 5.6volts. I am surprised how many guys get away with 6.0volts and sometimes more. On all my 4.8volt servos I never run more than a 4 cell nicad pack.

Why take a chance when there are now high voltage servos available for up to 2 cell lipo packs.

I speak from a little experience having been involved in the production of several thousand servos over the past 42 years.