What Effects Does a Car Charger for a Phone Have on a Car?

A car's power comes from several sources. When the car is turned off, lights inside the vehicle are powered by stored energy from the car's battery. When the car is turned on, the alternator produces energy the entire time and keeps the battery full, assuming that the vehicle is maintained and in working order. If there is a problem with the alternator, the battery may not charge properly while the vehicle is on, resulting in frequent dead batteries after power drainage.

Cell phone car chargers plug into the lighter socket or available power socket and allow the user to charge her cell phone drawing power from the car. If the car is turned off, just as with the lights inside the car, the cell phone charger is drawing power from the car's battery. Leaving the charger plugged in when not charging a cell phone may also drain the battery's power, but this will be a slower drain on the battery than if charging a phone. If the car is turned on, the cell phone is receiving power from the alternator, just like the rest of the car. The power generated from the alternator is essentially limitless, which means that charging a cell phone in a running vehicle is not a drain on power.

The outlet a car charger is plugged into draws its power from the battery. When the car is off, this power comes from the battery only. When the car is on, this power comes from the battery that is being kept fully charged by the running alternator. The alternator converts power from the gas into energy to keep the battery charged, so the charger is only indirectly drawing on the gas tank. This is, of course, assuming that the vehicle is well-maintained and in working order with no known power issues. The drain on fuel is essentially insignificant because the alternator is running if the vehicle is turned on, regardless of whether a phone charger is plugged in or not.