Microtek Heritage 600 UPS
Back lasts upto 1 or 2 seconds

I am Mohanraj from Coimbatore. I have bought Microtek UPS last year at first Battery Backup lasts upto 15minutes for 4 months but after that reduced to 10, 8, 5, 2 minutes respectively but now it lasts upto 1 second and what is the use of keeping UPS for system? I lodged complaint 13 days ago but upto this minute no response from the company. I dont know what to do?