History

To begin to explain this I have to go back in history. 

Tried adding battery pack and DCC circuit breaker: 1994

In 1994 I tried using a a battery pack to a decoder.  I used a DCC circuit breaker between the battery pack and the decoder's track input.  The battery pack was in a trailing car and plugged into a track power  When the decoder was on track power the circuit breaker cut the connection to the battery.  When track power was not available the circuit breaker allowed current to flow from the batter and the decoder would convert to analog power.  While it worked well it required a trailing car and when track power was turned off the locomotive would continue to run until the battery ran out of power.

Tried adding capacitors to decoders: 1995

In 1995 I demonstrated the concept of using capacitors and battery as an aux power input for DCC and also using radio as a potential source for delivering the DCC signal.  These were primitive concepts but had limited success.  I used six 4400uf capacitors to provide aux power to  the decoders.

These were great experiments and led to much thought, but frankly did not work to well for the following reasons.

1. You could not program the decoders with all the extra power because they drained the programming track.
2. When you had a short the locomotives that were stopped would move (in the analog conversion approach). 
3. The power source simply was not enough to make a real difference.
4. The real problem was DCC signal reception and this was not improved at all with the extra power source.
    

One alternative to all this was to transmit the DCC signal via radio. Air Wire 900 from CVP is an example of this concept and offers some excellent possibilities.

Radio control is an excellent approach but suffers from other disadvantages.  One key disadvantage is the lack of standards and thus the ability to select compatible products from a variety of manufacturers.