A flat battery is responsible for more UK roadside calls than almost any other single fault. Knowing how to jump start a car is a genuinely useful skill — it can get you back on the road in ten minutes and save you the cost of a callout when you’re in a safe location.
What You Need
You’ll need either a pair of jump leads and a running vehicle, or a portable jump starter pack (a small lithium battery device that connects to your battery and provides the starting current). Portable jump starters are excellent — they’re compact, they work without a second car, and they’re available for around £40–£80. Worth having in the boot.
Jump Starting with Jump Leads
1. Park the working car close to the flat battery car — engine off, both cars near enough for the leads to reach, but not touching each other.
2. Red lead first: Connect one red clamp to the positive (+) terminal of the flat battery. Connect the other red clamp to the positive (+) terminal of the good battery.
3. Black lead: Connect one black clamp to the negative (-) terminal of the good battery. Connect the final black clamp to an unpainted metal surface on the flat battery car — NOT to the negative battery terminal. An engine bolt or metal bracket is ideal. This reduces spark risk near the battery.
4. Start the working car and let it run for 2–3 minutes.
5. Try to start the flat car. If it doesn’t start after a few attempts, wait another 5 minutes before trying again.
6. Once the flat car starts, remove leads in the reverse order: black earth first, black from good battery, red from good battery, red from flat battery.
7. Drive the recovered car for at least 30 minutes to allow the alternator to recharge the battery.
Common Mistakes to Avoid
- Connecting the clamps in the wrong order
- Letting the clamps touch each other while connected to a battery
- Connecting the final black clamp to the flat battery terminal (fire/explosion risk from hydrogen gas)
- Giving up after one failed start — wait a couple of minutes and try again
When Jump Starting Won’t Work
If the battery is completely dead (showing less than 6V), some jump start methods won’t work. If the car won’t start after multiple attempts with a known-good donor car, the battery may need replacement, or there’s another fault.
In this situation, call Jam’s on 07369 205 703 and we’ll get you sorted.
*Jam’s Breakdown Recovery — available 24/7 across Milton Keynes and surrounding areas for battery problems, jump starts and all roadside assistance.*
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