Click (Volkano VK9100WT UPS not a good product)

I bought a Volkano constant series mini UPS VK9100WT about 6 months ago. I was initially told that the lasting power during loadsheding was 4 hours. This was 6 months ago. 6 months later it does not evan last 1 and a half hours during loadshedding. Can somebody please advise why this is happening????????