The short answer is that it depends heavily on your car's battery health and the type of lights, but with a healthy battery, standard halogen headlights can typically last 2-4 hours before draining the battery to a point where the car won't start. LED lights, being more efficient, might last 8-12 hours or more. However, repeatedly doing this will significantly shorten your battery's lifespan.
The main factor is your car battery's capacity, measured in Amp-hours (Ah). A typical car battery has a capacity of around 45-60 Ah. The "draw" of the lights determines how quickly this capacity is used up. For example, a pair of halogen headlights (low beams) can draw about 10 amps, while interior dome lights draw only 2-5 amps.
Here’s a quick reference table based on a common 50Ah car battery in good health:
| Light Type | Estimated Power Draw | Estimated Runtime (Engine Off) |
|---|
| Halogen Headlights (Low Beam) | ~10 Amps | 4-5 hours |
| LED Headlights | ~5 Amps | 8-10 hours |
| Parking Lights / Tail Lights | ~4 Amps | 10-12 hours |
| Interior Dome Light | ~2 Amps | 20-25 hours |
| LED Daytime Running Lights | ~1 Amp | 40-50 hours |
It's crucial to understand that these are estimates. An older battery, cold weather, or other parasitic drains (like a security system) will drastically reduce these times. The safest practice is to never intentionally leave your lights on with the engine off. If you accidentally leave them on, a portable jump starter is a valuable tool to keep in your trunk. Modern cars often have automatic headlight shut-off features to prevent this exact problem.
