If you are really serious about high current to servos and compatibility with receivers - -
Consider that Radio Shack (and others) sell small PC boards that have holes on a grid that happens to match the pin spacing of servo connectors.
Headers are also available, as well as various parts from  hansenhobbies.com.
You make short servo cables that connect the receiver to the PC board, and install either short cables with male pin servo connectors, or headers on the PC board The battery is then connected to the PC board. The power buss is on the PC board, and if needed, a capacitor or two across the power buss. This allows servo current to bypass the receiver.
It also makes it easier to use a receiver with multiple models.
Common servo wire color codes
White or yellow  Servo control signal
Red  Positive power  (4.8 to 6v or so)
Black or Brown negative power/common

When using multiple batteries, remember that the batteries must be of equal voltage, the closer the better.
They do not have to be of equal storage capacity, but should be of similar cells. (has to do with internal resistance of the cells)
More elaborate devices are sold for a price, and usually used on such things as giant scale models.
It's possible to use decoupling diodes to make the batteries more independent, but usually not needed.