It's hard to pinpoint the issue without more information. You may just need to replace the batteries. I encourage you to reach out to Eaton (Eaton purchased Powerware about 6 years ago). Here is the product page where you can download the manual: http://powerquality.eaton.com/Products-services/Backup-Power-UPS/9355.aspx?cx=3
Here is the contact info.
Toll Free: 1 800 843 9433 International: +1 919 871 1800 E-mail: [email protected]
It either means the ground wire in extension cord is not there or is open. It could also mean that the outlet wasn't wired with a ground back to the panel.