How to Tell If Your Alternator Is Not Charging
The alternator charges the battery and powers electrics while running. A weak one confuses many people because its symptoms mimic a weak battery.
Signs
A battery light on the dash, dimming/flickering lights, general weak electrics, or the car dying shortly after a battery disconnect.
Normal numbers
With the engine running, voltage should be ≈ 13.7-14.7 V. Below ~13 means weak charging; above ~15 means overcharging (a faulty regulator).
Testing
Measure voltage while running with a voltmeter or via OBD2. Mowtar AI shows system voltage and alerts if it leaves the normal range.
FAQ
How to tell alternator vs battery?
A weak battery: slow start then runs. A weak alternator: runs then electrics fade/die. Measuring charging voltage settles it.
Drive with the battery light on?
Only a short distance; if the alternator is not charging the car will stop when the battery drains.