For some reason, Apple decided only to warn users that the mouse battery level was low when it hit 2%.
BTT has a setting 'Warn if battery level is below...". I have it set to 20% but it never has worked. Also, it shows the current battery level at being 0%, no matter what the level of charge.
The functionality to get an early warning when the battery level of my mouse is running low (before it gets to the 2% which is pretty late) is the whole reason I bought the BTT. Now that it is not working, it is pretty useless for me.
//ahh apple must have changed something again, the old way to retrieve the battery state doesn't work anymore in the latest mojave release... will include a fix in the next version.
Seems like this is showing 0% still in the latest version of MacOS. Would be super useful if this feature can come back to avoid having to rig something manually! (But appreciate it's a small one.)