Mc Farland--------Here is a decent battery setup- that's not too cost intensive.
Use dual batteries (6V packs ) -both plugged into the RX.
If possible use HD switches /connectors .
avoid cheap connectors and std AWG long leads. get 22 AWG if possible
You don't ned to rewire directly to each servo - but on a BIG plane for max flow to multiple 200 in oz ganged servos -- get a power buss.
if possible - buy some Sanyo 1950ma -or other Sanyo super high discharge NIMH cells . get em in 6v packs
Robotic Solutions as well as other battery specialist suppliers can furnish these .
You don't need meters or anything else to determine if your present batteries are able to supply enough current .
Simply listen to the sound of the servos operating the surfaces with your pack -vs a BIG pack or one pack vs two packs
The pitch (tone ) will get higher as more current is supplied to the servo - try this with 4.8 vs 6 to note how much this factor affects the pitch.
The servos are designed to operate on 6 Volts NOT MORE. so if you are thinking of directly wiring in higher voltage - forget it