I configured low battery to be 20% and critical to be 10%, but the only notification that ever shows up is a critical warning at 5%. I enabled plugging and unplugging notifications and those work as expected, but performing the same steps with the low battery warning does not, and it still works off an incorrect level. It also does not appear to track battery percentage when sleeping, although I suppose there’s nothing to do about that one.
It won’t. If you’re worried the battery will end during sleep setup hybrid sleep: SystemSettings > EnergyManagement > EnergySaving > WhileSuspendingHibernateAfterACertainTime. The default is 3 hours. This can be changed in /etc/systemd/sleep.conf
As for KDE not giving the correct notifications, does it track discharge correctly? I have a problem in my laptop, which is the battery charge state not being tracked, sometimes. And this results in the absence of notifications. I have a small script I run whenever I notice the battery icon is not changing, so I know the charge state at the moment. However, your problem seems different. I can post the script later if you want though.
It does track discharge correctly, as far as I can tell, but it doesn’t notify the user based on it.
On my laptop I get notifications (when it’s properly tracked).