Eddie,

As mentioned above, the voltage regulators we have available specifically for model use (and proven in jets) are linear regulators and the voltage is dropped from the higher to the lower basically resistively so that the extra energy is dissapated as heat. What is needed for high cell counts is essentially a "switching power supply" which operates much like a switching speed control for electrics. These DC-DC converters have very high efficiency, and can even "up convert" a lower voltage to a higher one, or even a negative one. For example, you can find DC-DC converters that generate +12V and -12V from a 5V power supply.

Unfortunately, not many of these have been adapted or proven in the RC market. Here is one that is capable of supplying 3.5A loads that has been:

http://www.medusaproducts.com/Other/...-BEC-45035.htm

Note that it doesn't have a heat sink. Its efficient enough that it doesn't need one. I have the 2A model in my TRex helicopter and it works flawlessly, however, I'm not sure I'd want to be the first guy to try one in a jet, even if 3.5A was a sufficient current rating for that application...

Bob