A battery discharged message or a flashing battery bar graph on a Smart-UPS UPS indicates that the reported runtime remaining is at or within 2 minutes of the Low Battery Signal Time. Its basically telling you that within 2 minutes of going to battery power, the UPS will be in a low battery state, and will issue graceful shutdown commands to any computers running PowerChute software, and are configured to monitor this particular UPS.
If you have increased your load recently, the runtime may have dropped wo within 2 minutes of the low battery signal time. It also could be an aging battery that isn;t providing the runtime it once was able to.
The knowledge base document below goes into much more detail about the causes and potential solutions for this condition.