Light left on in the car: what now?
Left the car lights on for too long and the battery is flat? Not a problem! We'll show you how to safely jump start your car and what you should do now.Light left on in the car: what now?
If you leave the lights on in your car for too long, the battery can quickly discharge – regardless of whether you have halogen, LED or xenon lamps. In most cases, however, you do not have to call the breakdown service immediately. A neighbour or acquaintance often helps. Our guide shows you what to do if your car battery goes flat.
How long can you leave the lights on in the car?
If you accidentally leave the lights on in the car, it may still be able to start the next morning. But how long can you actually leave the lights on in the car before the battery goes flat?
Most car batteries have a capacity of 45Ah and a vehicle electrical system voltage of 12V. This means that if you have left the lights on in the car and two small 10W bulbs stay on, it will take 27 hours for the battery to go flat.
However, this will only be the case if the battery is new and fully charged – an unlikely scenario. The battery lifetime is often considerably shorter and can also be adversely affected by external factors such as cold.
If the car does not start: This is what you should do
For many drivers, this is the absolute nightmare: The car lights have been left on overnight, the battery is flat in the morning and the vehicle will not start. This is not always a case of having to call the breakdown service. Instead, you can simply ask a neighbour or a friend to help jump start your car with jumper cables.
To do this, proceed as follows:
- If your vehicle is parked on a road, take safety measures first by setting up a warning triangle and/or by wearing a high-visibility safety vest. You will need a jumper cable to bridge the terminals.
- Now take the red jumper cable and connect it to the positive pole of the battery in the other car.
- Next, attach the red cable to the positive pole of your car battery.
- Then connect the black cable to the negative pole of the battery in the other car.
- Connect the other end of the black cable to the vehicle earth – do not connect the cable to the negative pole of your car battery as this may cause sparks!
- Now ask your helper to start the other car.
- Wait one minute then start your vehicle.
- If the car does not start, wait few minutes and repeat the procedure two more times.
Start a car
If the car starts, do not immediately switch the engine back off – the car will fail to start again. To be on the safe side, you should drive your car for between 10 and 20 minutes, preferably without running power guzzlers like the seat heating. By this time the car should have ‘recovered’ and you can switch off the engine without worrying that it won't start again afterwards.
If the car does not start after the third attempt, you should not make any further attempts to jump start your battery – otherwise this may result in costly damage. In such a case, it is best to call the breakdown service, who will in the vast majority of cases be able to start your battery with a booster. You should then drive the car for at least 10 minutes before switching off the engine again.
If you have left the car lights on for a very long time, the battery may also completely discharge. Although extremely rare, it is still possible. If this happens, the battery must be recharged. It is best to go to a car workshop for this, where you will be charged a minimal cost. Under no circumstances should you charge the battery via the mains supply at home – i.e. from a socket – as this is dangerous and could potentially have fatal consequences!
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