I have just discovered that I can connect my UPS to my NAS with a USB cable such that the NAS detects when the UPS is running just on battery power. This enables me to direct the behavior of my NAS (QNAP 251+) in response to this condition after a user specified period of time … either shut down completely or go comatose … both options ensure that the power outage does not outlast the battery life in the UPS and thus allows for a graceful power down.
It’s a shame it took a power outage longer than the battery life of my UPS for me to discover this feature. It was a long day watching the NAS do a health check.