A rapid "tick-tick-tick" when you turn the key (or press start) means the starter motor solenoid is trying to engage but doesn't have enough power to spin the engine. 9 times out of 10 it's a flat or failing battery.
The 60-second test that tells you which fault it is
Before anyone spends money, do this on the driveway. Switch the headlights on with the engine off, then turn the key or press start and watch the lights. - **Headlights dim heavily or go out as it clicks** — the battery is flat or has a dead cell. This is the answer roughly seven times out of ten. - **Headlights stay bright and you get one loud single clunk** — the battery is fine and the starter motor or its solenoid is at fault. - **Headlights stay bright and you get rapid machine-gun clicking** — the solenoid is chattering because it cannot hold in. Almost always a poor connection: corroded terminals, a loose clamp or a failed earth strap rather than the battery itself. - **Absolutely nothing, no lights, no click** — completely dead battery, a blown main fuse, or the main earth strap between engine and body has corroded through. That one test splits an £8 fix from a £350 one, and it takes less time than reading the rest of this page.
Why a clicking starter is nearly always a power problem
A starter motor needs an enormous amount of current — 150 to 400 amps on a cold morning, more on a big diesel. The solenoid on top of the starter is an electromagnet that pulls a heavy copper contact across to feed that current through, and it also shoves the pinion gear into the flywheel. The solenoid itself only needs a few amps to operate. So when there is enough power for the solenoid but not enough for the motor, the solenoid pulls in, the voltage collapses, the solenoid drops out, the voltage recovers, and it pulls in again. That cycle repeating twenty times a second is exactly the clicking you hear. This is why a car that clicks will still light the dashboard, work the radio and flash the indicators. Those loads draw a couple of amps. Cranking is a different world.
Battery, terminals or starter — how a mechanic decides
With a multimeter, the numbers are unambiguous. A rested battery should read 12.6 to 12.8 volts. At 12.2 it is half flat, at 12.0 it is effectively dead, and below 10.5 volts while cranking the battery cannot do the job even if it looks charged. The test that catches the batteries everyone else misses is the load or conductance test — a proper tester puts a real load across it and reads internal resistance. A battery with a shorted cell can sit there showing 12.4 volts and still collapse to 8 volts the instant the starter turns. Most tyre and battery shops do this free in five minutes. Voltage drop is the other one. With the meter across the negative battery post and a bare bit of engine block, crank the engine. Anything over about 0.3 volts means your earth path is the problem, not the battery. Do the same on the positive side to the starter feed. If the battery is healthy, connections are clean and voltage drop is low, and you still get a single clunk with no rotation, the starter motor is the fault.
What you can fix yourself in twenty minutes
1. **Clean the terminals properly.** White or blue-green fluffy powder is corrosion and it acts like an insulator. Disconnect negative first, then positive. Wire-brush both posts and clamp interiors back to shiny lead, refit, and nip the clamps up so they will not twist by hand. 2. **Check the clamps are actually tight.** A clamp you can rotate on the post is a clamp that cannot pass 300 amps. This alone fixes a surprising number of "dead" cars. 3. **Follow the earth strap.** There is a thick braided or black cable from the negative terminal to the body, and another from the body or battery to the engine or gearbox. Look for green corrosion, fraying or a rusted bolt. They are cheap and they are a genuinely common failure on cars over ten years old. 4. **Jump start it correctly.** Red to the flat battery positive, red to donor positive, black to donor negative, black to a bare metal bracket or engine lifting eye on the flat car — not to its negative post. Leave the donor running for five minutes before trying. 5. **Then drive it, do not idle it.** A flat battery needs 30 to 45 minutes of actual driving to recover meaningfully. Ten minutes on the drive does nothing. One old trick with a caveat: tapping the starter body firmly with a hammer while someone turns the key will sometimes free stuck brushes and start the car. It works, but treat it as a way to get home, not a repair.
If it starts after a jump but dies again later
That tells you the battery is not holding charge or is not being charged. Two very different bills. If the battery warning light stays on or flickers while driving, or the headlights pulse with the revs, suspect the alternator. A healthy charging system reads 13.8 to 14.6 volts at the battery with the engine running. Below 13.2 it is not charging properly; above 15 the regulator has failed and it is cooking the battery. If charging voltage is fine but the car is flat every few mornings, you have a parasitic drain — something staying awake after lock-up. Common culprits in UK workshops are an aftermarket dashcam hard-wired to a permanent live, a failing boot or bonnet switch keeping a lamp on, a dying stereo amplifier, and on VAG and BMW models a comfort or gateway module that will not go to sleep. Measuring it properly needs a clamp meter and patience, so budget an hour of diagnostic time.
UK costs in 2026
Fitted prices at an independent garage, including VAT: - Terminal clean and refit: £15 to £40, often free if you are already there - Earth strap replacement: £40 to £90 - Standard 60Ah battery supplied and fitted: £85 to £150 - AGM or EFB start-stop battery, coded to the car: £150 to £290 - Starter motor: £180 to £450 on most family cars; £400 to £900 where it sits under the inlet manifold, which covers a lot of modern diesels and V6 petrols - Alternator: £220 to £550 - Parasitic drain diagnosis: £60 to £120 for the first hour Two things worth knowing. Start-stop cars need the new battery registered or coded to the charging system, otherwise it is charged to the wrong profile and dies early — that is a scan tool job, not a spanner job. And a mobile battery fitter is often cheaper and quicker than a recovery callout if you are certain the battery is the fault.
Cold weather, short journeys and why it happens in December
A battery loses roughly a third of its cranking power at freezing point, while a cold engine with thick oil needs considerably more current to turn over. A battery that was quietly failing all summer gets found out on the first frost. Short journeys make it worse. Starting the car uses a big chunk of charge, and a ten-minute run to the shops does not put it back. Do that five days a week through winter with heated seats, lights and a rear screen on, and the battery is slowly discharging every single day. If your car sits for long spells, a £30 smart trickle charger left on overnight once a week will add years to the battery's life and is far cheaper than the recovery truck.
Why does my car click but not start? — The starter solenoid is engaging but there is not enough current to spin the motor. In most cases the battery is flat or has a failed cell; the rest of the time it is a corroded terminal, a bad earth strap, or a worn starter motor.
Is rapid clicking the battery or the starter? — Rapid repeated clicking is almost always a power supply problem — flat battery or poor connection. A single loud clunk with bright headlights points at the starter motor or solenoid instead.
Can a car battery be dead but still show 12 volts? — Yes, and it catches people out constantly. A battery with a shorted or sulphated cell can read 12.2 to 12.4 volts at rest and still collapse under the 200 to 400 amp load of cranking. Only a load or conductance test proves it.
How long does a car battery last in the UK? — Typically four to six years. AGM start-stop batteries used mainly on short town journeys often only manage three to four, because they never get fully recharged.
Will jump-starting damage my car? — Not if it is done correctly — red to red, black to donor negative, and the final black clamp onto bare metal on the flat car rather than its battery post. Avoid jump-starting a modern start-stop car from a revving donor engine, as the voltage spike can damage electronics.
How much does a starter motor cost to replace in the UK? — £180 to £450 fitted on most family cars. Where the starter is buried under the inlet manifold — common on modern diesels and V6 petrols — labour pushes it to £400 to £900.
My car started fine yesterday and just clicks today. What changed? — A battery does not fail gradually in a way you notice; it fails on the coldest morning after weeks of getting weaker. Cold temperature plus thicker oil raises the current needed just as the battery's ability to supply it drops.
Do I need to code a new battery to my car? — On any car with stop-start, yes. The battery management system needs to be told a new battery has been fitted and what type it is, otherwise it uses the old charge profile and the new battery will not last. It requires a scan tool.
Can a bad earth cause clicking? — Absolutely, and it is often missed. The starter's return current goes through the earth strap, so a corroded or broken strap gives exactly the same rapid clicking as a flat battery while everything else on the car still works.