If your vehicle's volt gauge doesn't show that your vehicle is charging correctly, then check the following:
Check all the wiring at the rear of the gauge.
To access the speedo from the back, open up the bonnet to access the rear of the dashboard.
Check wires are all plugged in and in order. Use the codes on the wires, against the chart below to match their location on the dashboard. (You can also download this chart below).
Check to see if the alternator is charging the battery.
Access the alternator under the rear tray.
Check alternator is charging by testing voltage at battery with engine running. RPM may need to be raised to 1,200 and re-check - because not all alternators will
If faulty replace. You can purchase a replacement alternator here.
Check to see if the battery is faulty.
Check battery under the bonnet.
Check connections and for signs of damage.
Load test battery.
If battery is faulty, then replace.
Check all the wiring from the battery to the alternator.
Check all the wiring and connectors from the battery and the alternator.
Look for damaged wires and connectors.
Make sure all components are mounted securely to the vehicle.
Check the earth cables.
Check the alternator mounting bolts and bracket. Tighten if necessary.
Check the battery mounting bolts and bracket. Tighten if necessary.
Check earth cable from engine to frame.Check earth cable from battery to frame at front of vehicle.