Why does Windows display Your Battery is Very Low notification when the Battery has 100% charge?

Windows has been displaying a notification intermittently for two days now that my battery is very low, and that I should plug in my computer. It's a desktop for one thing, not a notebook, and it is plugged in. In the Battery Saver settings the battery shows as having 100% charge. The TrippLite battery backup LED shows full charge as well, and says that it's getting 123V. The notification takes over my screen and shows up right in the middle of the screen. I'd like to know how to correct this Windows error.

Question by Tim on Super User, licensed CC BY-SA. We show a short excerpt and link to the original thread as credit.