I finally found a solution to the problem, only one single man on earth had have ever before 
After hours of searching, I came across an extension which finally had an switch for that battery tray icon:
It's called "Just Perfection" and is more powerful then only to hide the battery icon, but tbh I didn't try all the stuff inside.
For me, the look of my system tray is now as demanded:
I again thank everybody and especially @Aravisian for supporting and pointing me in the right direction
