13.8 v
13.8 V shows that in any case the alternator is charging, otherwise the voltage measured directly at the battery terminals would be closer to 12 V.
It does not explain however, the sudden voltage drop to 5V or slow drainage of the battery. If all the electric connections are in order, it would take quite a heavy load (closer to a shortcut) for the battery voltage to drop from 12 to 5V. That would not go unnoticed. It is therefore more likely that somewhere an electrical connection is intermittently failing. Crucial is to know where this 5V is measured.
After the battery has had time to "recover", does it crank normally or is the starter motor barely turning over?
|