I’ve posted this problem before.
But now both threads are too old and besides I finally was able to get more information.
When battery is charging, if I let it reach 100% and unplug, battery icon on taskbar decreases now to 30% after few seconds. Again, it fixes by rebooting and the issue can be avoided by not letting the battery charge 100% (unplugging at 99%, for example).
While with the issue, tried “acpi -b” in terminal and noticed it gives indeed the correct readings in percentage and remaining time. Then compared acpi’s and taskbar icon’s remaining time readings, and they coincided (or at least close). Moreover, I observed that acpi’s percentage reading decreases with usual speed when battery is discharging, but icon’s reading decreases much slower from that 30%, so in the end both behave really according to the time remaining (both percentage readings reach critically low battery level at roughly the same time). So the issue is specifically with the taskbar icon’s percentage reading.
Then if I plug again battery icon shows percentage increase equally slow, but when battery reaches full charge icon suddenly changes to 100% again, then the cycle repeats the same.
Now I remember this issue started to happen few years ago, while current openSUSE version was 11.3, just when I updated KDE version. Then it happened with every coming openSUSE release until now, all doing clean installations. Both on KDE and GNOME.
Hope this time someone can get an idea…