I noticed that the application doesn't always report the battery percentage of the earbuds or the case when they're not connected:
When I have both earbuds in, it shows their battery percentages but the case as 0%:

When I put on airpod back into the case, its battery drops to 0% but the case then shows 255%:

After a few moments, the battery of the case drops down to 0% as well:

Checking against my phone, the airpods had the right percentage shown when they were in my ears and the case was at 86%.
ps. this was tested on the HEAD of the /linux/rust branch on NixOS (with the Asahi kernel, running Hyprland) and with AirPods Pro 3s