I believe Matt was erroneously referring to lee's regulated supply as a resistor box. To (try to) clarify, the box Lee's building would take a wide range of incoming voltages and convert the incoming voltage down to 5.2 volts for the jb3. It does this by using a voltage regulator on an integrated circuit chip.
The car adaptor is designed to only be fed 12 volts. Thus, unless it uitilizes a voltage regulator similar to that Lee's using, it would not properly reduce an incoming voltage of other than 12 volts down to the 5.2 needed by the jb3. Lee's adaptor would allow folks to use non-12-volt batteries such as the 9.6v and 7.2v rc car packs and the ubiquitous wallmart 9v lithium ion battery to directly power their jb3s
Very interested in hearing how long a single wallmart 9v would power both a ua5 (with phantom on) and a jb3