I will try the Naztech. Is 18v the magic number? Is there a voltage +/- variance that I have to work with?
Edit to add from the manual:
7. EXTERNAL POWER
The SONOSAX SX-M2 can also be powered from an external DC source, from 12
to 24 Volts, via the "DC IN" connector.(Battery powering is automatically disabled
once an external DC source is used.) Once the external power supply is connected,
the SX-M2 may then be operated as when powered by batteries or accumulators. If
the "ON" led flashes normally (every 3 seconds), the external voltage is between 14
to 24 Volts. If it flashes every second, the external voltage is below 14 Volts.
Polarity : + = center, - = outside collar