How to Jump-Start a Car Safely — Step-by-Step Guide

A flat battery is one of the most common breakdowns in the UK. Here's the exact sequence for jump-starting safely without damaging your car's electronics.

A flat battery can strike without warning — left overnight in cold weather, or simply because a light was left on. Jump-starting is a skill every driver should know.

What You Need

A set of jump leads (at least 2.5m long, 16mm² gauge)

A running donor vehicle with a healthy battery

Both vehicles on level ground, engines off

The Correct Connection Order

Always connect in this exact sequence:

1. Red clamp → flat battery positive (+)

2. Red clamp → donor battery positive (+)

3. Black clamp → donor battery negative (−)

4. Black clamp → bare metal on the flat car's engine block (not the flat battery negative — this avoids sparks near the battery)

Starting Up

Start the donor vehicle and let it run for 2–3 minutes. Then attempt to start the flat vehicle. If it starts, leave both engines running for at least 5 minutes before disconnecting.

Disconnecting — Reverse Order

Remove clamps in the exact reverse order:

1. Black clamp from engine block

2. Black clamp from donor negative

3. Red clamp from donor positive

4. Red clamp from recovered vehicle positive

After the Jump-Start

Drive the recovered vehicle for at least 30 minutes to allow the alternator to recharge the battery fully. If the battery goes flat again within days, it needs replacing.

When Not to Jump-Start

Do not attempt a jump-start if: the battery is cracked or leaking, there is a strong smell of rotten eggs (sulphur), or the vehicle has been submerged in water.

If you can't get a jump-start to work, Fred's Towing Services provides fast roadside assistance across Newport, Cardiff, Bristol and Bath. Call 01633 982028 — available 24/7.