Starting · Quick guide

🔋 Car Won't Start? Try a Jump Start First

Difficulty: Easy Time: 10–15 min Tools: Jump leads, donor vehicle or battery pack

The most common reason a car won't start is a flat 12V battery. Before you call breakdown cover, it's worth trying a jump start — it costs nothing and takes about 10 minutes.

EVs and PHEVs: Jump starting a full electric vehicle is different — do not connect jump leads to the traction battery. The 12V battery in an EV can be jump started normally, but check your handbook first. PHEVs vary by model.

Signs it's a flat battery (not something else)

  • The car clicks rapidly when you turn the key but doesn't turn over
  • The engine turns over very slowly and dies
  • Nothing happens at all — no lights, no dash, completely dead
  • The interior lights work but dimly

If the engine cranks normally but doesn't fire, the battery is probably fine — you may have a fuel, ignition, or sensor issue instead.

How to jump start correctly

Order matters. Get it wrong and you risk damaging electronics or causing a spark near the battery.

  1. Position the donor vehicle close enough for leads to reach — engines don't need to be touching.
  2. Red lead: dead battery positive (+) first, then donor battery positive (+).
  3. Black lead: donor battery negative (–), then an unpainted metal part of the dead car's engine block — not the negative battery terminal itself. This reduces spark risk near the battery.
  4. Start the donor vehicle and let it run for 2–3 minutes.
  5. Try starting the dead vehicle. If it doesn't start first time, wait another 2 minutes and try again.
  6. Once running, disconnect in reverse order: black from engine block, black from donor, red from donor, red from your battery.
  7. Drive for at least 20–30 minutes — ideally motorway speed — to let the alternator recharge the battery properly.
Battery packs: A portable jump starter pack (around £30–£60) is worth keeping in the boot. They work the same way but without needing a second vehicle.

When a jump start won't fix it

If the battery won't hold a charge and goes flat again within a day or two, one of three things is happening:

  • The battery is old and needs replacing (most batteries last 4–6 years)
  • The alternator isn't charging the battery while you drive
  • Something is drawing power when the car is parked — a parasitic drain
PAD 12V battery test: A professional load test tells you whether your battery still has capacity or needs replacing — not just whether it has enough charge to start. £25, mobile across Pontypridd and RCT. 12V battery check →
Battery not holding charge?
Find out if it needs replacing.

A professional load test tells you the battery's actual cold cranking amps and state of health — not just whether it has enough charge to start. £25, mobile across Pontypridd and RCT.

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