The red LED indicates your UPS is reporting a fault. According to the series of lights lit up above the battery bar graph on the right hand side, this UPS is reporting an inverter fault, meaning something has malfunctioned with the internal component in the UPS that converts the DC battery power generated by the battery to AC power that is output by the UPS.
The recommended next step is to perform a brain dead of the UPS, which I will outline below:
1. Turn off the UPS.
2. Unplug it from the wall.
3. Unplug all load from the output receptacles.
4. Disconnect all batteries, including any extended run battery packs.
5. Wait 10-20 seconds and reverse the process to turn the UPS back on.
If this does not fix the issue, the UPS will need to be replaced.
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