Is there a way to automate adding/removing device tags?

I'd gladly compose an RM rule for you that watches current battery status of any given device, and generates a date-stamped report whenever the percentage jumps back up (e.g. on battery change). But I'll agree that a dedicated app is warranted here.
In the meantime, don't overlook existing tools like Tile Builder, to group things together in a dashboard setting for quick reference.