The cold temperature and higher demands of lights and heaters put added pressure on batteries, leading to a seasonal spike in cars failing to start, usually at a hugely inconvenient moment.
So here’s our advice on how to deal with a flat battery, including the methods to get it going again and how to deal with problems in automatic cars, hybrids and EVs.
Jump start using jump leads
Jump leads are the safer and easier way to try to get a car with a flat battery started. They are safe to use on manual, automatic and hybrid cars, as well as EVs which have lost the charge in their 12V battery.
Before you do anything, check the flat battery isn’t damaged or leaking. If it is, jump starting could cause further damage or injury so don’t even attempt it. Instead, have the battery replaced immediately.
To use jump leads you’ll need a set of good quality leads (obviously) and a car with a similar sized or larger engine. Position the cars close enough that you aren’t over-stretching the jump leads but that the cars aren’t touching.
- Ensure all electrical systems such as lights, wipers, radio and heaters are off.
- Remove any loose metal objects from near the batteries and remove any loose clothing that could get caught in the engine.
- Connect one end of the red jump lead to the positive (+) terminal of the working car’s battery, then connect the other end to the positive (+) terminal of the flat battery. Connect one end of the black jump lead to the negative (-) terminal of the working car’s battery and the other end to an earthing point on the other car - this needs to be a solid, paint-free metal point such as a bolt or bracket away from the battery.
- Start the working car and let it run for a few minutes to feed some energy into the flat battery. After one or two minutes, try to start the car with the flat battery. If the battery is seriously depleted this may take several attempts.
- Once both cars are running, leave them connected for about five minutes then remove the leads. You do this in the reverse order to how you attached them - “flat” car negative first, then the negative of the working car followed by the positive of the flat car and lastly the positive of the working car. Make sure the leads don’t touch any metal surfaces or get caught in the engine’s moving parts.
- Drive the failed car for at least 15 minutes, preferably longer, in normal conditions - ie not heavy traffic - to recharge the battery. If the battery fails again after this, it could be a sign of a bigger problem with the battery or the car’s alternator.
Jump starting an electric car or hybrid
The rise of electrified vehicles has slightly complicated the old-fashioned jump start as cars with more than one battery become more common.
However, even hybrids and EVs have a basic 12V battery to power ancillary systems such as heating and lights, as well as vehicle management systems, and if this is flat these cars won’t start.
Jump starting an EV’s 12V battery works in the same way as in any other car. Connect the leads in the correct order and allow some power to trickle through to the flat battery before trying to start it. The only tricky bit may be locating the 12V battery in the first place, so refer to the owner’s manual for your specific vehicle.
Some hybrids can be jump started in the same way as a conventional car but some work slightly differently.
Toyota and Lexus hybrids have a dedicated jump start positive terminal, usually located under the fuse box cover, and you should use this rather than the positive battery terminal.
In some Kia and Hyundai hybrids built after 2018 a 12V lithium-ion battery is used instead of a standard lead-acid starter battery. These should never be jump started. Instead, there is a battery reset switch which should be pressed. If you are in any doubt, consult you owner’s manual or your local dealership.
How to bump start a car
If you don’t have access to a set of jump leads or another car to help boost your battery you can try bump starting it. However, this is a trickier and more dangerous method and it only works on cars with a manual gearbox.
To do this you’ll need help to push the car and someone to operate the ignition.
- First, put the car in second gear and turn on the ignition.
- Get your helpers to start pushing the car and once the car reaches at least 5mph let out the clutch quickly. This should engage the transmission and the turning of the wheels should then help start the engine spinning.
- Once the engine is running, stop the car but leave the engine running for at least 15 minutes.
How to avoid a flat battery
Prevention is better than a cure so there are some steps you can take, especially in winter to stop your car battery going flat.
- Try to park in a garage or other sheltered area to protect the battery against harmful sharp changes in temperature
- Switch everything off at the end of each journey, including lights, heater, heated windscreens, radio, and disconnect any phone chargers or other devices plugged into 12V sockets
- Check the terminal connections are tight and free of dirt or corrosion
- If your battery is more than four years old or showing signs of struggling have it checked by a professional