You must use the 8A MAX relay on the base unit to control the power to the in-vehicle computer. This way, the computer receives power only when the ignition is on.
You must power the in-vehicle computer through the base unit auxiliary 8A MAX relay. This way, the tablet computer and the base unit both react to the vehicle ignition signal, after a configurable delay. The tablet then runs on its own battery for a duration configurable in Windows.