SmartUPS ES 350 frequently shutting down

[AaplMike]

Hello. My SmartUPS ES 350 is shutting down a couple time per month, which brings down my server and NAS drive. It happened again today at 9:15, and to be honest, this is happening WAY too frequently to depend on it. When it shut down today, the log said there wasn't enough battery power and immediately shut off. However when I checked it from the server after everything came back up, apcaccess shows that there is PLENTY of time on the battery given the load...

MODEL : Back-UPS ES 350
STATUS : ONLINE
LINEV : 120.0 Volts
LOADPCT : 11.0 Percent
BCHARGE : 98.0 Percent
TIMELEFT : 22.9 Minutes
MBATTCHG : 8 Percent

The log entries:

Oct 8 09:17:31 proxmox apcupsd[4679]: Power failure.
Oct 8 09:17:32 proxmox apcupsd[4679]: Battery power exhausted.
Oct 8 09:17:32 proxmox apcupsd[4679]: Initiating system shutdown!
Oct 8 09:17:32 proxmox apcupsd[4679]: apcupsd exiting, signal 15
Oct 8 09:17:32 proxmox apcupsd[4679]: apcupsd shutdown succeeded

Now, here's the problem. there was NO disruption of utility power at all today. Why is the UPS detecting one? the circuit isn't overloaded, and it's not GFCI. I replaced the battery 6 months ago. As far as I can tell, the unit is defective.

Has anyone else experienced this? Is it a known issue with this unit?