Microtek ups,no backup,pc restarts on voltage...

Question

I've a microtek 800 VA double battery (each having 7.2AH) ups.  suddenly before 4 days a low battery like alarm  came and my speaker (intex) burnt out.After that  ups is not providing any backup (before problem it was providing around 50 minutes backup) and also pc restarts with a  little voltage fluctuation with a sound from ups.ups is 1.5 year old.please  help me.