The problem is what I describe in the title of the topic, a battery that I don’t know where it is appears in the “Device Viewer” section and because of this it also appears in the battery icon on the system tray.
I would rephrase this to “a battery that I don’t know where it is”, since the PC cannot find things that don’t exist
Details about your existing hardware in use, might have helped us to make a better guess.
From the little info you have posted, my magic crystal ball says the battery is inside a drawing assistant hardware, either embedded or external.
Don’t worry, it’s not my first language either.
I have checked the manual when I have increased the ram and changed the wifi module, there is only one battery with a single cable that powers everything.
PS: It must be a KDE Plasma Bug because it doesn’t happen to me in Gnome.
It is not uncommon that some touchpads or other devices have an internal battery, which is seen by the system as a battery, not being able to have more info.
In your posted image, there is a clue, in the name of that battery. ELAN is a known driver for pointing devices, like a touchpad.
I have no other reason to talk about this . It’s your hardware. You should know, or your vendor would.