Failing UPS

I bought a UPS to ensure power supply during loadshedding. In the first month I could get 2hours of power from it. Second month it dropped down to 1hour and later to a mere 17minutes. I returned the UPS and was given "a new one," but the same thing happened.

I took it back again. I was accordingly refunded, but that was not the intention. My desire was to have a reliable device that would last me for at least 12months.