Check for warning lights (battery/charging) on the dashboard
Inspect battery terminals and alternator wiring for looseness, corrosion, or damage
Check battery voltage with a multimeter (engine off)
Normal resting voltage: about 12.6 V (fully charged)
Start the engine and measure charging voltage at the battery terminals (engine running)
Normal charging voltage: about 13.8–14.7 V
Turn on electrical loads (headlights, blower, rear defroster) and re-check charging voltage
Voltage should typically stay above about 13.5 V
Perform a belt/drive check (if applicable)
Verify alternator belt is present, tight, and not slipping or cracked
Check alternator output current (if you have a clamp meter)
Compare to vehicle specifications if available
Check for alternator ripple/AC output (advanced)
Measure AC ripple with a multimeter; excessive ripple indicates a bad rectifier
Check alternator warning/field control wiring (if applicable)
Verify proper voltage/control signal at the alternator connector
Check for stored diagnostic trouble codes (OBD-II)
Look for charging system or alternator-related codes
If voltage is low (below spec) or unstable
Test alternator stator/rectifier (as applicable) or have alternator tested at an auto parts store
If voltage is high (above spec)
Check voltage regulator (internal or external) and related wiring/ground connections