The calculated backup time is based on certain fixed parameters and they vary time to time in the real world.

  1. The load power is not exactly shown on the document and changes from time to time depending on operation modes
    1. Operation environment, especially temperature impacts the battery capacity
    2. As we know, the UPS is purchased to secure the power supply when main is gone. In practice, people purchase the UPS with backup time more than the target. Considering this, it’s not necessary to get a very accurate calculated backup time