Letsseehere… the battery in my cell phone is 3.4w. A 500 CCA car battery stores about 6000 watts. So you could completely recharge your cell phone at least 1000 times before you actually drain the battery to a point that the car wouldn’t start.
The amount of energy small electronics is pretty insignificant compared to the amount of energy needed to turn an engine over. I’ve accidentally left my satellite radio on for weeks and the car still started.