- A flat or weak battery is by far the most common reason a car will not start.
- Short trips, cold weather and a battery older than 4 years all speed the problem up.
- A jump starter solves the immediate breakdown. After that you check why the battery went flat.
- Does the battery go flat again soon after a jump start? Then the battery is not the only cause.
You turn the key and nothing happens. Or you hear a weak, slow clicking sound. You are not alone: a flat or weak battery is the most common cause of breakdowns. But it is not the only possibility. These are the five most common causes and what you can do right away.
Cause 1: flat battery
You recognise this by a slowly turning starter motor, a clicking sound, or no response at all while the lights and dashboard still work. Causes: standing still too long, leaving the lights on, or too many short trips where the battery never fully recharges. Solution: jump start with a jump starter or jump leads, then drive for at least 20 minutes so the alternator can top the battery up.
Cause 2: worn or faulty battery
If the car starts after a jump start but is flat again after a day of standing still, the battery is probably at the end of its life. Batteries last 4 to 6 years on average. A garage or car parts shop can test the battery, often free of charge. On a worn battery a jump start helps temporarily, but replacement is the real fix.
Cause 3: faulty starter motor
If you hear a hard, short click but the engine does not turn over, or if jump starting does nothing while the battery is full, the starter motor may be faulty. That is a mechanical problem you cannot fix yourself, so book it in at a garage.
Cause 4: fuel problem
Does the engine turn over but not fire? Then there may be no fuel, a blocked fuel filter or a problem with the fuel pump. First check whether the fuel gauge really is not on zero. This also needs a garage if jump starting has no effect.
Cause 5: fuse or electrical problem
No sign of life at all when you turn the key? Check the fuses. Your manual states which fuse belongs to the starter motor. A blown fuse you can replace yourself. For a larger electrical problem you need diagnostic equipment.
Frequently asked questions
How do I know whether my battery is flat or dead?
A flat battery recharges through the alternator or a battery charger, after which the car starts normally. A dead battery goes flat again quickly, even after charging. The most reliable test is a professional battery test at a garage, which measures the health of the cells and not just the voltage.
What do I do if jump starting does not help?
If the car still will not start after a correct jump start, the battery is not the cause. Most likely: a faulty starter motor, a fuel problem or a larger electrical problem. In that case call roadside assistance or a garage.
How long does it take to recharge a flat battery through the alternator?
On the motorway a completely flat battery charges enough for the next start in 30 to 60 minutes. Short trips around town are not enough: they use more power than the alternator produces. For a full charge you are better off with an external battery charger.
Can I test the battery myself?
With a multimeter you can measure the voltage: a healthy, full battery reads 12.6V or higher. Below 12.0V the battery is flat, below 11.5V there may be cell damage. A real battery test that measures capacity is done at a garage, because voltage alone does not tell you enough.
When does a battery need replacing?
After 4 to 6 years on average, depending on use. Signs: the battery goes flat quickly after standing still, the car starts slowly in the cold, or the battery test shows low capacity. Have it measured if in doubt. A new battery costs less than an unexpected call-out.
