Ground wire issues. Locate the ground wire that connects the battery to the frame or engine. Make sure it is clean and tight. If the ground wire is loose or corroded, replace it.
Bad starter. A bad starter can draw too much power from the battery, causing low voltage. Check the starter to make sure it is working properly.
Defective alternator voltage regulator. The voltage regulator controls the amount of voltage output by the alternator. A defective voltage regulator can cause the alternator to produce too little voltage or too much voltage. Check the voltage regulator to make sure it is working properly.
Failed diode in the alternator. Diodes prevent the flow of current in one direction. If a diode fails, it can cause the alternator to produce low voltage. Check the alternator's diodes to make sure they are working properly.
Damaged wiring. Look for any damaged wires in the charging system. If there is any damaged wiring, replace it.
