Before you start
- Jumper cables (booster cables), or a charged portable jump starter
- A second car with a working battery of the same voltage (normally 12 V)
- Your owner’s manual (some cars have special jump points)
Is it the battery?
A flat battery usually shows these signs when you turn the key or press Start:
- A rapid clicking sound, or nothing at all.
- The engine turns over very slowly.
- Dashboard lights are dim or flicker.
If the engine turns over normally but won’t start, the problem is probably fuel or ignition, and jump-starting won’t help.
Method 1 Prepare both cars
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Step 1: Check the manual
Look up the jump-starting section. Some cars, including many hybrids and cars with batteries in the boot or under a seat, have dedicated jump terminals under the bonnet.
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Step 2: Position the cars
Park the working car close enough for the cables to reach, nose to nose or side by side, but not touching. Turn both engines off, take the keys out, and apply the parking brakes.
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Step 3: Switch everything off
Turn off lights, radio, heater fan and other electrics in both cars.
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Step 4: Inspect the battery
Don’t jump-start if the flat battery is cracked, leaking, swollen or smells of rotten eggs. Get professional help instead.
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Step 5: Find the terminals
The positive terminal is marked + and often has a red cover. The negative is marked −. Clean off heavy white or green corrosion with a dry cloth if it stops the clamps gripping.
Method 2 Connect the jumper cables in order
Never let the clamps touch each other while any cable is connected.
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Step 1: Red to the flat battery
Clamp one red clamp firmly onto the + terminal of the flat battery.
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Step 2: Red to the good battery
Clamp the other red end onto the + terminal of the working battery.
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Step 3: Black to the good battery
Clamp one black end onto the − terminal of the working battery.
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Step 4: Black to bare metal on the dead car
Clamp the last black end to an unpainted metal bolt or bracket on the dead car’s engine block, or its marked earth point, at least 30 cm (1 ft) from the battery. This keeps any spark away from battery gases.
Method 3 Start the cars and remove the cables
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Step 1: Run the working car
Start the working car and let it idle for 3–5 minutes to put some charge into the flat battery. Raising the revs slightly can help.
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Step 2: Start the dead car
Try to start the car with the flat battery. If it doesn’t start, wait another few minutes and try again. Don’t crank for more than 10 seconds at a time.
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Step 3: Remove in reverse order
With both engines running, remove the black clamp from the dead car’s metal, then black from the good battery, red from the good battery, and finally red from the formerly flat battery.
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Step 4: Keep the engine running
Drive for at least 30 minutes, ideally on faster roads, so the alternator can recharge the battery. Avoid switching off straight away.
Method 4 Use a portable jump starter instead
Booster packs are handy because you don’t need a second car or another driver.
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Step 1: Charge it in advance
Keep the booster pack charged (check it every few months) and store it in the car.
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Step 2: Connect it
With the booster turned off, connect red to the battery’s + terminal and black to bare metal or the − terminal, following the booster’s instructions.
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Step 3: Start the car
Switch the booster on, start the car, then switch the booster off and disconnect black first, then red.
Troubleshooting
The car still only clicks
Check the clamps have a firm metal-to-metal grip, wait longer with the working car running, or try thicker cables. The battery may be too far gone, or the starter motor may be faulty.
The car starts but dies again later
The battery isn’t holding a charge, or the alternator isn’t charging it. Get both tested before your next trip.
The cables get hot
Stop immediately, switch off and disconnect. Thin, cheap cables can overheat; use heavy-gauge cables.
Frequently asked questions
How long should I drive after a jump-start?
At least 30 minutes of normal driving. Short trips may not recharge the battery enough for the next start.
Can jump-starting damage my car?
Done correctly, it’s safe. Connecting the cables the wrong way round can damage electronics, so follow the order carefully and check the manual for any special jump points.
Can I jump-start in the rain?
Yes, 12 V systems are low voltage, but keep the clamps and battery as dry as you can, and take extra care with your footing.
Summary
Connect red to the flat battery’s positive, red to the good battery’s positive, black to the good battery’s negative, and black to bare metal on the dead car. Start the working car, wait a few minutes, start yours, remove the cables in reverse, and drive for half an hour. If it keeps happening, get the battery and alternator tested.
