Miles Tracker, Car, Battery, Charge, Drain
Any car battery will drain if the car isn't used for a while. Things like the alarm will constantly use up power, so you should make sure you run your engine at least once a month or keep the battery on a trickle charger.
The Miles Tracker will periodically use your car's battery when the engine is off, to ensure it's still connected with our network. That said, it uses such little power that it'd take several months to drain an average car battery by itself.