Hello Les..................I'm building a TF Sea Fury and I have two Futaba 9252 in my elevator and rudder. You can use a 6v rx battery as long as It's regulated down to about 5.3v. I will probably use the MPI MAXX Products voltage regulator ACC134N, it has a jumper you can cut to change from 6v. down to 5.4v output regulation. I'm refering to a Nicad RX Battery.
Ihave an extra Align 6A Bec that chops the voltage to around 5.8v, and if Iadd the step down it will cut it down to 5.1v. Ibelieve that even a fully charged 4 cell nicd/nimh can be around 5.6~5.8v, so Iassume running a regulated 5.8v should be no problem for the 9252's. Ijust have a fear that with a 4.8v pack Irisk the chance of a brownout or other issue regarding low voltage situations.
Imay just get some 6v servos to replace the 9252's and just run a 5 cell nimh.
Happy Holiday's
Les