If you leave your lights on while the car is parked for a few hours and have trouble starting it why?

Answer 1

The battery has only so much energy available. Headlights use a lot of energy. If you leave them on for any amount of time with the engine not running, less energy will be left in the battery to turn the starter. This is normal and to be expected. The older the battery, the less energy it can store. So if the battery in your car is old, it will make the problem worse.

Answer 2

Leaving the lights on can drain the car's battery, leading to difficulty starting the vehicle. The battery may not have enough power to start the engine after being drained by leaving the lights on for an extended period.