The alternator charges the battery and powers the electrics while the engine runs. When it fails, the car runs on battery alone until that is empty, and then it stops.
Warning signs
- Battery or charging light on the dashboard, even if it flickers.
- Dim or flickering headlights, especially at idle and getting brighter when you rev.
- Whining or grinding noise from the front of the engine that changes with revs.
- Electrical oddities. Slow windows, a weak stereo or a flickering dash.
- Repeated flat battery even after a replacement.
- Burning smell from a slipping belt or an overheating alternator.
Alternator or battery?
The two get confused all the time. A simple rule: if the car starts after a jump but dies soon after, the alternator is more likely. If it will not hold a charge but runs fine while driving, the battery is more likely. A proper test with a meter settles it in minutes.
Do not wait
Driving until it stops can leave you stuck on a busy road. If you notice these signs, get it tested while the car still runs normally.