The alternator charges your battery and powers the car while the engine runs. When it starts to fail, people often blame the battery, replace it, and end up stranded again. Here is how to spot the real culprit.
Dimming or flickering lights
If your headlights or dash lights dim at idle and brighten when you rev, the alternator may not be producing steady power. Flickering interior lights are another clue.
The battery warning light
The battery shaped light on the dash is really a charging system light. If it comes on while driving, the alternator is likely not charging, and the car is running on battery reserve.
Electrical glitches and a weak start
Slow windows, a resetting radio, or a car that cranks slowly a day after you charged the battery all point to a charging problem rather than the battery itself.
How to confirm it
With the engine running, a healthy charging system reads about 13.8 to 14.4 volts at the battery. Much lower means the alternator is not keeping up. A multimeter makes this a two minute test.
Frequently asked questions
Can I drive with a failing alternator?
Only a short distance. Once the battery reserve runs out the car stalls, so head straight to help.
Will a new battery fix it?
No. A new battery just delays the problem because the failing alternator will drain it too.
Keep a charger and a jump starter handy. See our battery and charger guides.
