UPS battery reaches a critical level.

I've several Home windows XP Professional SP3 Computers in the same office, each linked to a Back-UPS ES 550. I am getting this issue with three (to date) from the five Computers there:
Whenever that there are any energy drop, the most imperceptible energy blip that nobody at work even notices, the Computers are immediately purchased to hibernate.
In every PC's Energy configurations, I've assemble them to ensure that they're going into hibernation whenever the ups replacement battery reaches a vital level. "Critical level" is understood to be 17% from the battery charge.
Diagnostics in every situation reveal that the batteries are OK. Actually, on all these three Computers I disabled the hibernation setting, disconnected the UPS in the wall plug as the PC was running, and went laptop computer on battery energy for up to ten minutes before inserting the UPS in. No batteries reported a drop to anywhere close to the designed critical level.
Among the UPSes continues to be service for around 2 yrs coupled with its battery changed in December. The 2nd UPS is a touch more than a year old. And also the third UPS only has experienced service since March. They are each supporting identical Hewlett packard minitower Computers with identical flat-panel shows. Among the UPSes will also support a little Wi-fi compatability entry way. Otherwise, little else is blocked in to these devices' battery shops.
What's leading to this, and just how will i repair it?