the dm speedcal does draw power from the cig lighter circuit when keyed off if wired per instructions. You can wire it to a switched 12v source and it will work the same. That being said I think the draw on one of these is very low and shouldn't be draining the battery in a weeks time. Anytime i know the car going to be sitting for a while I hook it up to the trickle charger so i've never had any issues other than this last time from the obd2 adapter when the charger wasn't hooked up.