The installation manual for the XTL is VERY specific about how to install the radio with a remote head, which wires need to have power remain hot at all times and what the voltage parameters are required to be.
In short, the red lead from the radio drawer and the red lead from the control head must BOTH remain hot at all times and go to the same source. The grounds (black wire) from the drawer and the head must BOTH go to the same ground point. The yellow ignition sense wire from the control head, in order to function correctly must go to a true igntion source, and must go low or very close to zero volts when the car is off.
ANY voltage differentital between the two red leads will cause unpredictable results in operation. When wired correctly, there should be neglibible power drain when the unit is off.
MAINTENANCE MODE - REMOTE DEVICE
If you have FW version R17.00 or newer, but NOT R19.60 and experience this issue when operating or powering up the XTL mobile, upgrade your firmware to the newest revision. This is a known firmware issue caused by a bug in the firmware release.