Jump-Starting and a Flat Battery

How to recognise a flat battery

• Turning the key or pressing the start button does nothing, or just clicks
• The starter motor turns very slowly
• The dashboard lights are dim or go out when you try to start
• Central locking no longer responds

Why the battery goes flat

• Cold: in frost a battery delivers less power, but the engine needs more.
• Short trips: driving only short distances barely recharges the battery.
• Age: capacity fades after a few years.
• Lights or accessories left on: a forgotten parking light is enough.
• Long standing time: even a parked vehicle uses power, for example for the alarm and control units.

Jump-starting step by step

For a jump-start you need a second vehicle with a similar battery voltage and jump-start cables. An overview:

1. Both engines off, ignition off. Don't let the clamps touch each other.
2. Red cable to the positive terminal of the flat battery, then to the positive terminal of the donor battery.
3. Black cable to the negative terminal of the donor battery, the other end to a bare metal part on the engine block or an earth point of the stranded vehicle, not to the negative terminal of the flat battery.
4. Start the donor vehicle and let it run briefly, then start the stranded vehicle.
5. Remove the cables in reverse order. Then drive for a longer stretch so the battery recharges.

Common mistakes

• Cables swapped: positive to negative can destroy the electronics.
• Black cable straight to the negative terminal of the flat battery: this can cause sparks at the battery.
• Running it too briefly: switching off right after starting means you'll soon be stuck again.
• Jump-starting an obviously damaged or frozen battery: don't do this.

When you should call us

• You don't have a second vehicle or cables
• You're somewhere dangerous (motorway, tunnel, underground garage)
• The vehicle still won't start despite jump-starting; there may be another fault
• It's a hybrid or electric car

We try jump-starting the vehicle on the spot first. If that doesn't work, we take it to a garage.

Preventing it next time

Have the battery checked, especially if it's already a few years old. Avoid repeated short trips in winter, or recharge the battery occasionally with a charger. Breakdown cover can also be worthwhile, since it covers roadside assistance.