Citace ze stránek APC :Manual Calibration: Ensure Battery is charged to 100% before beginning Calibration Stop the Power Chute software from running and disconnect the serial, USB, or Ethernet cable(s). There must be at least a 30% load attached to the UPS during this procedure, and this load cannot fluctuate more than +/- 5%. THIS IS IMPORTANT Attach a non-critical load to the UPS and then force the UPS on battery by disconnecting it from utility power Allow the unit to run on battery until it turns off completely. The load attached to the UPS will drop. If the Load is not at least 30% or if the calibration is ended before the UPS drops the load, the calibration will not work. Plug the UPS back into the wall outlet and allow it to recharge (preferably turned off)