How do I Repair My UPS?

Hello, I Have an Apollo Brands UPS.
I Use It Last 3 Years, First Time It Can Backup 30-40 Minutes.
Now It Is Down And Give Me Low Backup Under 5 Minutes.
I Charge It 4-5 Hours Regularly But It Don't Give Me Backup What I Want.
Now I Suffer Very Low Backup And I Lose Sometime My Important Document.
What Can I Do Now?
