I have a UPS which is configured with Apcupsd. It shows all the stats correctly. The problem is that when I switch to battery mode, something sends a shutdown signal to the PC. My guess is that it might have something to do with the power utility from system settings. It can see when it's charging, and when I plug it out it shows for about 16 minutes of battery life, but it's shutting it down anyway. Can it be disabled?
I think by default, ubuntu is configured to shut down or hibernate when battery reaches critical level. This could be the source of your problem.
Try disabling the critical battery level automatic shutdown as shown here - http://looselytyped.blogspot.in/2012/04/preventingdisabling-automatic.html