Problems with battery

You have an intermittent charging problem and the alternator was tested while it was working. That is very commonly due to worn brushes inside the alternator. 80,000 miles is a little soon for that unless you drive on a lot of dusty roads.

The clue is found by measuring the voltages on the two small wires plugged into the back of the alternator, but they must be measured while the engine is running, and to mean anything they must be measured while the problem is occurring. One will have full battery voltage. The other one must have less but not 0 volts. If you find 0 volts on only the second wire, the brushes are open. That always starts out as an intermittent problem. I just replaced mine last fall for $9.00 and an hour of my time.

They changed the circuit on some models so you might find 0 volts on one wire, then considerably less than battery voltage on the other one. The important thing is the voltage on one of those wires must be around 4 - 11 volts. Let me know what you find.