Dell UPS 500W Charger Fault or battery disconnected

Dell UPS 500W reports a Charger Fault/failure or battery disconnected.

Pull the batteries out, take the plastic case off, disconnect the batteries from each other and check voltages. if any battery are 1 volt or more different from the others:

One battery reads between 12.5 to 13.1 volts and the other reads 11 volts or lower the lower reading battery may be bad. Try charging it on a 12 volt battery charger for an hour or 2 if it goes back to the original reading or quickly goes below 12 volts it is bad.

Replace both batteries batteries.

On the UPS clear the error if it does not clear itself. Press and hold the left arrow button, then go through the menu until you find the option to clear the error log and reset error condition.