What is the reason for the headlights being on for 20 minutes but the car not starting?

[DeCecilia]

The reasons why the headlights are on for 20 minutes but the car does not start are as follows: 1. Insufficient battery voltage: When the battery voltage is insufficient, the horn and lights can still work, but the car may not start. Specific detection method for low car battery voltage: Use a multimeter voltage range to test the battery voltage. If it is below 10V, consider replacing it; if it is around 11V, it can be used temporarily, but be prepared to replace it; if it is above 12V, it can be used normally. 2. Check the quality of the gasoline and carbon deposits: If the car has been driven for about 20,000 km, focus on checking the throttle, ignition switch, starter, fuel pump, sensors, and other components related to the starting and fuel supply system. 3. Starting too quickly: After powering on, do not start immediately. Wait for thirty seconds to one minute before ignition to see if it has any effect.

[DelBrayden]

I've been driving for many years and have encountered the situation where the headlights are on but the car won't start several times, mainly due to a depleted battery. Leaving the headlights on for 20 minutes continuously discharges the battery. If the battery itself is old or severely drained, there won't be enough current to start the engine. Another factor is an issue with the charging system, such as a faulty alternator not charging the battery, which accelerates power loss when the headlights are on. Check if the battery terminals are loose or corroded, or use a multimeter to measure the battery voltage—if it's below 12 volts, it means the battery is dead. An emergency solution is to jump-start the car, but it's best to maintain the battery regularly, testing it every six months to avoid draining it unnecessarily in cold weather. This issue can be quite dangerous—if it happens at night, pull over safely, turn on the hazard lights, and handle the situation after ensuring safety.

[SanAlina]

I think the issue usually lies with the battery or alternator. Leaving the headlights on for 20 minutes drains a significant amount of power, and a small battery capacity can easily be depleted. At this point, starting the engine requires high current, but the power supply falls short. It could also be a chain reaction from other system failures, such as poor starter contact or circuit issues, though these are less likely. I recommend first trying to jump-start the car using jumper cables connected to another vehicle. If that doesn't work, you should have a professional shop inspect the charging system—check if the alternator belt is loose or if the voltage regulator is faulty. As a habit, always turn off the lights during short stops and keep the battery terminals clean.

[CharlotteDella]

This is most likely due to a dead battery. Leaving the headlights on for half an hour can drain one and a half batteries, especially in cold weather when battery performance is poor, making it more difficult to start the engine. I once experienced this when I forgot to turn off the lights and was left in a panic. There could also be an issue with the charging system, such as a malfunctioning alternator failing to recharge the battery in time. For immediate action, seek help for a jump start or use an emergency power source, and check if any fuses have blown. For prevention, consider regular battery replacement or voltage testing, and maintenance every two years to avoid such incidents.