I have a 5+ year old CyberPower UPS (1000PFCLCD). The software installed on my PC indicates the unit is operating correctly, the battery is fully charged and it has at least 20 minutes of reserve and the present load. However, when there were recent power interruptions everything went off instantly. When I did the test on the unit every went down instantly. Any advice? My initial thought was just an old battery, but the unit is showing the battery fully charged. I was reluctant to replace the battery and find the unit itself is toast.