Earlier quoted context omitted.
Most (all?) decent datacenters also have generators on site, and the intent is that the UPS will never run out of charge. So the fully-discharged case is an error and it might be intentional to require intervention to recover.
Yeah, some people treat UPSes as "backup power" but that's not really what they're intended for. Their intended purpose is to bridge the gap during interruptions... either to an alternative power source, or to a powered-off state.
a) If the power is out too long for your UPS (or you have solar and batteries and they discharge overnight or whatever) that the system will turn back on when the power recovers, and
b) You will not have extra bonus outages just because the UPS is in a bad mood.