Three different parts produce a 'car won't start', and they cost very different money. Fitting a new battery when the alternator is the culprit wastes a day and a hundred-plus euros — the new battery will be flat again within the week. Here is the triage we run on the phone, in plain English.
Listen to what the car does
- Single loud click, then nothing — lights still bright: usually the starter motor (solenoid engaging, motor not turning). The battery may be fine.
- Rapid machine-gun clicking, lights dim with each click: classic flat battery — enough power for the solenoid, not enough to crank.
- Slow, laboured crank ('rrr… rrr…'): a weak battery, cold weather, or corroded terminals. Often revivable — but test it, because a battery that cranks slowly when warm is on its way out.
- Cranks normally but never fires: not a battery problem at all — fuel, spark or immobiliser. A jump-start won't help.
- Absolutely nothing — no dash lights, no click: a very dead battery, a loose or corroded terminal, or a blown main fuse.
The battery-light clue
If the battery warning light stayed on while driving before the failure, suspect the alternator: the engine was running off the battery, draining it. The giveaway pattern is a car that jump-starts fine, drives twenty minutes, then dies again — the battery was never being recharged.
What a proper test measures
- Resting voltage: a healthy 12 V battery reads about 12.6–12.7 V engine off; below ~12.0 V it's substantially discharged; below ~11.8 V it may not crank.
- Cold-cranking performance (CCA): a load or conductance test shows whether the battery can still deliver its rated punch — this is the number age destroys.
- Charging voltage: with the engine running, roughly 13.8–14.4 V at the battery means the alternator is doing its job; much less and the alternator (or its belt) is the problem.
Why we test before we sell
Our technicians carry a tester and a multimeter and run exactly these checks at your car before recommending anything. If the verdict is starter or alternator, we tell you so — the diagnostic call-out costs you a diagnosis, not a battery you didn't need. If it is the battery, the correct replacement is on the van and fitted on the spot.