Uninformative field from UPS used for determining HWP spin down

[ktcrowley]

During 11/7/2025 power outage, when confirming what the logic of the hwp-supervisor agent is to set the "spin OK" variable to stop, I found that the agent uses the UPS-reported estimated_minutes_remaining field. This field appears to be equal to 0 mins for several UPSes currently active at site.

As an alternative to this, a minimum battery percentage remaining could be used, or a "time since outage began" to avoid tripping the HWP spin-down safety maneuver during a brown-out or a power glitch. Otherwise, this field could be investigated on the UPSes themselves to determine how to make it meaningful.