I converted all my planes to A123,
two cells, that i bought separately and soldered together with a balance port, gives a voltage of 6.6V - no regulators needed, simply connect it to the receiver and there you go.
one of the main advantages of A123 is the durability and safeness of these cells, it allows me to locate the batteries at such a way that i dont need to take them out of the plane for charging.

another advantage that i found (due to the very stable voltage) is with my RAM500 turbines, which are very sensitive to battery voltage - just plugged a 2 cells A123 , set the minimal voltage down to 6.3V, and the turbine never missed a start ever since.
no burnt plugs, no false starts.