Whether you’ve accidentally left your lights on or your battery has reached the end of its life, a flat battery can happen to any driver. Fortunately, knowing how to jump start a car safely can help get you back on the road quickly.
In this guide, we’ll explain how to jump start a car step-by-step and highlight some important safety precautions along the way.
For more vehicle maintenance advice, visit our maintenance guidance hub.
What You’ll Need
Before you begin, make sure you have:
- A set of jump leads (one red positive lead and one black negative lead)
- Another vehicle with a fully charged battery
- Protective gloves
- Safety goggles
1. Locate Both Batteries
Park the vehicle with the charged battery close to the vehicle with the flat battery.
Make sure:
- The vehicles are not touching
- Both cars are on level ground
- There is enough space to safely connect the jump leads
Once parked, switch both vehicles off and locate their batteries.
2. Put On Safety Equipment
Before handling any battery connections:
- Put on your gloves
- Wear safety goggles
- Remove any loose jewellery
Batteries can produce sparks during jump starting, so taking basic precautions is important.
Once you’re ready, open both bonnets and ensure the battery terminals are visible and accessible.
3. Connect the Jump Leads
It’s important to connect the leads in the correct order.
Connect the Positive Leads
- Connect one end of the red lead to the positive (+) terminal of the charged battery.
- Connect the other end of the red lead to the positive (+) terminal of the flat battery.
Connect the Negative Leads
- Connect one end of the black lead to the negative (-) terminal of the charged battery.
- Connect the other end of the black lead to a solid metal earth point on the vehicle with the flat battery.
Do not connect the final black lead directly to the flat battery’s negative terminal.
Instead, attach it to an unpainted metal part of the engine bay, away from the battery and fuel system.
4. Start the Vehicles
Start the engine of the vehicle with the charged battery and allow it to run for a minute or two.
Then attempt to start the vehicle with the flat battery.
If it doesn’t start immediately:
- Wait a few minutes
- Check the jump lead connections
- Try again
If the vehicle still won’t start after several attempts, the battery may need replacing or another fault may be present.
5. Leave the Engine Running
Once the vehicle starts successfully:
- Leave both engines running for around five minutes
- Allow the flat battery to build up some charge
When you’re ready to disconnect the leads, remove them in the reverse order:
- Black lead from the grounded metal point
- Black lead from the charged battery
- Red lead from the flat battery
- Red lead from the charged battery
Take care not to allow the clamps to touch each other during removal.
Take the Car for a Drive
After disconnecting the jump leads, take the vehicle for a drive.
Driving helps the alternator recharge the battery and may prevent another flat battery shortly afterwards.
If the battery repeatedly goes flat, it may be time to investigate further or consider replacing it.
When a Flat Battery Becomes a Bigger Problem
Sometimes a flat battery is a one-off issue.
Other times, it can be a sign of:
- An ageing battery
- Electrical faults
- Charging system problems
- General vehicle deterioration
If repair costs are starting to mount up, it may be worth assessing whether the vehicle remains economical to keep on the road.
Another big problem can be exhaust problems. If your exhaust doesn’t sound too healthy, and you suspect blowing exhaust problems, check out our article here.
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