Written by the workshop at Alan Dawson Autoworks & Recovery · Updated 31 July 2026
How do you tell a flat battery from a dead starter motor?
Listen and look. Rapid clicking with headlights that dim badly is a battery. A single heavy clunk with the lights staying bright is a starter, because the power is clearly getting through but nothing turns.
The reason is simple. A weak battery can just about pull the starter solenoid in, but the moment it tries to spin the engine the voltage collapses, the solenoid drops out, and it repeats: that is the machine-gun clicking. Because the voltage is collapsing, the lights dim in time with it.
A failed starter is the opposite. Voltage stays up, the lights stay bright, the solenoid engages with one clunk, and then nothing happens because the motor itself or its brushes are gone.
A quick test: switch the headlights on and try to start. If they dim dramatically or go out, suspect the battery. If they stay steady while the engine refuses to turn, suspect the starter.
What are the signs of a failing alternator?
The red battery warning light staying on while you drive, headlights dimming at idle and brightening when you rev, electrics behaving oddly, or a car that starts on a jump and then dies shortly afterwards.
The alternator recharges the battery and runs everything electrical once the engine is going. When it fails the car runs on the battery alone, which lasts anywhere from a few minutes to half an hour depending on what is switched on.
A common trap: the battery gets replaced because the car would not start, it works for a few days, then the same thing happens. The battery was flat because the alternator never charged it. Testing the charging system before buying a battery saves that.
If the light comes on while you are driving, turn off the heated rear screen, air conditioning and anything else you do not need, and head somewhere safe rather than continuing a long journey. If it stops, our recovery line is answered around the clock.
Is it safe to jump start a modern car?
Yes if you do it in the right order and use good leads, but on modern cars with sensitive electronics it is easy to cause damage. Connect positive to positive, then negative on the good battery to a bare metal earth point on the dead car, never to its negative terminal.
Earthing to bare metal away from the battery keeps any spark away from the hydrogen a charging battery gives off. Let the working car run for a few minutes before you try, and take the leads off in reverse order.
What to avoid: cheap thin leads that overheat, jumping from a running engine at high revs, and repeated attempts. If it does not start after two or three tries, something other than charge is wrong and more cranking will only flatten the good battery too.
If the car is a hybrid or electric, do not attempt it without checking the handbook. The 12V system is still there but the procedure differs and getting it wrong is expensive.
When do you need recovery rather than a jump start?
Any time the car will not run under its own power once started, when the fault is the starter or the charging system, or when you are anywhere unsafe. A jump start only solves a battery that has simply gone flat.
A jump gets you moving if the battery is the whole problem, for example lights left on overnight. It does nothing for a dead starter, a fuel or sensor fault, or an alternator that is not charging, because the car will stop again shortly.
It is also the wrong call on a hard shoulder or a busy road regardless of the fault. Getting the car off the road first is safer and usually faster than standing over it, and a flatbed does not care whether the engine runs. Read our guide on what to do when your car breaks down for the roadside order of play.
