Larry,

Yes, your charging system has failed, but don't go buying parts before finishing the diagnosis.
You have a meter? If no, go get one.
Measure the battery voltage.
Fire the engine. Measure again.
Measure between the center of the isolator and the plate. Should be 14+ with the engine running. Less than that check alternator connections.
Engine Off. Headlights on.
Measure between the battery + and the terminal on the boost contactor. Same as the battery?
Same for the battery - and the aluminum ground plate where things are mounted. Same? Ok connections are good.
Engine off.

If you were good to there, pop the wires off the islator and set the meter to resistance. May be marked as Ω.
Check between the center and both others one way and then reverse the test leads and do it again. If you don't get a difference one way and not the other, things are good.
Isolator failures are rare, but do happen.

Good luck Be sure to tell us what you find.

Matt