the gtech draws its power from the cig lighter...it doesnt use that to obtain its "stats".

also there is the 1st generation gtech which happens to be more accurate (but still off by like 0.1-0.2sec in the 1/4mile) than the 2nd generation gtech that was manufactured. it bases its "stats" from mercury i believe and uses it to calculate how quickly the car gets from point A to Point B.