I'm looking into a budget engine diagnostic system utilising a touch screen tablet.

My concern is the power consumption of the dongles when the engine is switched off.

I purchased a wifi dongle off eBay (software reports it as a Kiwi) and the unit continues to draw power when the ignition is switched off. Does anyone know if this presents a significant drain on the battery and would a bluetooth device be any better/worse?

A sign that doesn't bode well is that the unit gets warm during operation.