Key takeaway:
Whether using jumper leads with another vehicle or a portable jump-starter pack, following the correct safety steps and connection sequence will get your car running again without damaging electronics or causing injury.
1. Understand the Risks and Gather Equipment
Before attempting any jump-start, remember that car batteries:
- Produce explosive hydrogen gas
- Contain corrosive acid
- Deliver high currents capable of damaging electronics or causing burns
Equipment you’ll need:
- A pair of good-quality jump leads (red for positive, black for negative) or a fully charged portable jump-starter pack.
- Another vehicle with a healthy 12 V battery (if using leads)—avoid hybrids or EVs.
- Protective gloves and eye goggles.
- High-visibility clothing if stopping on the roadside.
2. Safety Precautions
- Park both vehicles on level ground with handbrakes applied and ignitions off.
- Remove keys, turn off all lights and electronics in both cars.
- Ensure that cables won’t dangle into moving engine parts and that no jewellery or loose clothing can short terminals.
- Never smoke or allow open flames near the battery.
- Inspect batteries and leads: do not proceed if either shows cracks, leaks, heavy corrosion, or damage.
3. Connecting Jump Leads
Follow this exact sequence to prevent sparks and surges:
| Step | Action |
|---|---|
| 1 | Open both bonnets and locate the battery terminals (consult handbook if needed). Ensure the positive (“+”) and negative (“–”) posts are clearly identified. |
| 2 | Clamp the red lead to the positive terminal of the dead battery. |
| 3 | Clamp the other end of the red lead to the positive terminal of the good battery. |
| 4 | Clamp the black lead to the negative terminal of the good battery. |
| 5 | Do NOT clip the other end of the black lead to the dead battery’s negative terminal; instead, attach it to a clean metal earth point (unpainted bolt or bracket) on the engine block of the car with the flat battery. |
4. Starting the Engines
- Start the donor car and let it idle for 2–3 minutes to build charge.
- Attempt to start the flat-battery car.
- If it doesn’t start within 5 seconds, switch off the ignition of the receiving car, wait 2 minutes, then try again.
- Once started, leave both engines running for 3–5 minutes to stabilise charging.
5. Disconnecting Jump Leads
Always remove cables in the reverse order of connection:
- Black clamp from earth point of dead-battery car.
- Black clamp from negative terminal of donor battery.
- Red clamp from positive terminal of donor battery.
- Red clamp from positive terminal of dead battery.
6. Using a Portable Jump-Starter Pack
Many drivers prefer a battery booster pack over jumper leads and a second car:
- Ensure the pack is fully charged and compatible (12 V).
- With pack switched off, connect the red cable to the positive terminal and the black to a metal earth point on the flat-battery car.
- Switch on the booster pack, then start the engine.
- After the car runs for 1–2 minutes, turn off the pack and remove leads in reverse order.
7. Bump-Starting (Manual Gearboxes Only)
As an emergency alternative (for manual transmissions):
- Ensure the car is in second gear, handbrake off, seatbelt fastened.
- Find a gentle downhill or get helpers to push the car to ~5 mph.
- Release the clutch swiftly while turning the ignition to “on.”
- If successful, the engine will fire; keep revs at 2,000 rpm for 1–2 minutes to charge.
Note: Modern cars with sensitive electronics may be damaged by bump-starting; use with caution.
8. Aftercare and Battery Health
- Drive at moderate speed for at least 20–30 minutes to fully recharge the battery.
- If repeated flat batteries occur, test voltage with a multimeter or have the battery’s health and charging system checked by a mechanic.
- Consider replacing batteries older than three years or showing signs of failing capacity.
Jump-starting correctly saves time and money while protecting both you and your vehicle. Always refer to your vehicle’s handbook for model-specific instructions and, when in doubt, seek professional assistance or roadside services such as RAC or AA.
