[ericbecky]

I would have expected the red light to come on by 120 miles as well.
You should be able to dump the data from your SD card and see how your system was utilized on your trip. (battery voltages, pack voltage, etc) Of course there is always the possibility that your red LED does not work. After a drive you can check the LEDs on the left side of the converter and confirm whether they coincide with the LEDs on the dash switch.

You can watch your stock Prius voltage via a scangauge. The Enginer system bases how many amps to put in based on the stock pack voltage (as opposed to SOC). as the stock pack voltage increases, the Enginer system ramps down the amps it is putting into the stock pack.