Servos are rated by all as either 3.7, 4.8, 6.0 or 7.4 volts.
The 4.8 and 6.0 was the standard till 5 years ago or so. at that time the common batteries were 4 and 5 cell nicad or NiMh packs. so for advertising the MFG stated all servos as 4.8- 6.0 volts as that is what the battery MFG showed on packaging.
MOST all 6.0 servos will handle a LiFe battery. I have found that some of the JR, Hitec, and Airtronic ones have burned up everynow and then. I would say one out of every 25-30 with the Life Packs. to me this just shows a bad servo from the beginning..
I only use LiFe Packs. I will never go back to Nicad or NiMh. no point. yeah you may say a NiMh pack is the same weight but it isnt. the guys runnign regulators are just a little scared to run with out them. We humans dont like change..
MJD the HS-65HB (karbonite gears) are very good servos. I buy them in bulk. i think they are the best 1/2A servo. now you can get other lighter ones that work great also.
so run the LiFe's they are the future...
If you are still running NiCads way behind in tech but who cares fly how you want. LiFe's are such a better battery.