Disconnect the battery
Inspect the alternator belt for wear, looseness, or damage
Check the alternator wiring and connectors for corrosion or looseness
Test the battery voltage with the engine off
Test the charging voltage with the engine running
Replace a damaged or worn belt
Tighten or replace loose or corroded electrical connections
Replace a faulty alternator fuse or relay
Replace worn alternator brushes or voltage regulator if serviceable
Replace the alternator if it fails charging tests
Reinstall all components securely
Reconnect the battery
Start the engine and recheck charging voltage