Have you tried skipping APC's software and just letting the MacOS handle it? I have an APC somewhat older than that, and while APC's software is rarely updated and flaky, I haven't bothered with it for years, since the MacOS's built-in Energy Saver pref pane recognizes the UPS and has no problems controlling things based on it. The same is true of a newer, smaller Green APC for my mini, and a beefy higher-end SmartUPS (also APC) on the server at work, so I'd expect that as long as your UPS has a USB connection, it'll also work without additional software.
Using the built-in software, you can check the battery level (and display it in the menu bar), set separate sleep/monitor/etc settings for when the computer is on battery, as well as shutdown times based on % of battery or minutes of runtime elapsed or remaining.