But it is pretty much the same as using 4 AA batteries.
Something else to keep in mind: If you use rechargeable batteries (NiCd, NiMh, LiPo, etc), each cell is usually 1.2 volts, so four AA cells in series will give you 4.8 volts.
Servos are generally designed to run on something like 4 to 6 volts, with their torque, of course, maxing out at 6 volts (don't run them on anything higher, though - you'll burn the driver circuitry and/or motors out).
Standard alkaline AA batteries are rated at 1.5 volts each; so 4 in series will give you 6 volts. If you want to use rechargeables, you will need to use 5 cells in series to get 6 volts, not 4 as with alkalines.
It may not seem like much, but that extra 1.2 volts equals a lot of torque gained or lost.
Unfortunately, I have yet to see a 5 cell AA battery holder...