If your car check battery indicator light up, can firstly check if the battery connecting wiring has oxidized, then check if the battery level is sufficient via the indicator on the battert. Normally green indicator mean the battery level is normal and black colour indicate insufficient power. If the battery is normal, it might be the alternator is faulty. A faulty alternator usually cause by below reasons:
1. Alternator belting loosen and skid, causing insufficient charge to the battery which lead to battery become undercharge and affecting its lifespan. It might even cause the battery unable to support your next engine start up.
2. Alternator rectifier faulty, causing the output voltage uncontrollable. Owner can obviously feel the headlamp brightness change intermittently when driving at night.
3. Alternator belting broken, alternator faulty, positive and negative terminal wiring broken will also cause the check battery indicator light up.
4. The carbon inside the alternator worn out or burnt will also cause the battery indicator light up.
Suggest to perform diagnose at work shop, usually the keypoints of diagnose are:
1. Check if the battery is faulty, replace if necessary.
2. Check if the alternator belting is broken due to aged, replace if necessary.
3. Check if the alternator wiring is open circuit or short circuit, replace if necessary.
4. Use measuring device to test the alternator see if its internal part is faulty. Replace if it is beyond repair.