TrippLite Frequency Fail

Tripp Lite Smart 1500 LCD, Frequency output while on battery = fail

This UPS failed during a recent outage, ie turned off instead of powering my one NAS from the battery. Outage lasted ~6 minutes.

After repeatedly attempting to reproduce the failure. I connected my oscilloscope to the unit while on battery and found the frequency to be ~119hz instead of the expected 60hz.

Similar tests with an inexpensive multimeter showed approx. 180hz.
Voltage shows ~117.

Connected a desk fan to the power supply, and in this video you can see/hear it slow down dramatically, when the UPS is switched to battery.