See battery percentage on the panel in Plasma 5.8

Question

It seems Plasma 5.8 cannot display battery percentage in the panel, as explained here.

I have found a solution and I am posting this in order to provide an answer.

Solution

As tested in Linux Mint 18.3 KDE:

The battery displayed in the Plasma 5.8 panel is part of the widget System Tray.

A separate widget is available called Battery Time which can add this option.

Click the Panel settings button, Add widgets > Get new widgets > Download new plasma widgets: there, search "battery", and install the one called Battery Time.

It can also be found at https://store.kde.org/p/1166501.

After that, go again to Panel settings, Add widgets, search and add Battery Time. By default it displays both percentage and time remaining, this can be changed in its settings.

To avoid seeing two batteries in the panel, hide the one in the system tray: click the panel settings button, put the mouse over the system tray, check the settings button there: either disable Battery and Brightness under General tab, or just hide it under Entries tab.

If one prefers to still see the system tray battery icon (which has the advantage of displaying more info, like the charging sign, and of providing more tools, like brightness level) and have a percentage level beside that, this setting can be used: go to System tray settings and disable Battery and Brightness under General tab; add a second System tray widget to the panel, and in its settings disable/hide all items except Battery and Brightness:

Then, disable the battery icon in the Battery Time widget settings and move the second tray and the Battery Time widgets close to each other.