Back-UPS RS 1100 shutting down

[Anonymous user]

Hi, I have a 'Back-UPS RS 1100' . It sometimes shuts down when the electric power is on with continuous beep. It happens every 4 -to- 6 hours of operation. But it runs fine on battery. Battery is good(it's a new set of batteries 4 months old) tested with multimeter ~ 27volts.

Symptoms :

• random shutdown after few hours of operation with continuous beep
• internal fan does not turn on when operating on AC power(even when the body becomes very hot) 
• internal fan does turn on during UPS mode on battery power
• load is a pc with max load below 500W

What might be the issue?

I am guessing it's a thermal shutdown of the unit, cause the plastic body becomes very hot to touch.