It sounds like the UPS may be having trouble switching between mains power and battery mode. Since you've already replaced the battery and checked the load, I'd check the input voltage and charging circuit next. If the issue keeps happening, getting it tested by a technician may be safer than continuing to use it. While you're waiting on a repair or replacement, you can also take a break with Geometry Dash on https://geodash.org/ a quick browser game that works well for short gaming sessions.
It sounds like the UPS may be having trouble switching between mains power and battery mode. Since you've already replaced the battery and checked the load, I'd check the input voltage and charging circuit next. If the issue keeps happening, getting it tested by a technician may be safer than continuing to use it. While you're waiting on a repair or replacement, you can also take a break with Geometry Dash on https://geodash.org/ a quick browser game that works well for short gaming sessions.