chiark-tcl-applet 1.0-2 (arm64 binary) in ubuntu groovy

 xbatmon-simple-tray is a battery status display, with useful
 tooltip, which sits in your system tray.
 .
 There is also an wrapper script, chiark-tcl-applet-wrapper, which
 can embed any X11 program in your system tray.
 .
 If you do not yet have an X11 system tray (eg because you are not
 running a desktop environment with panel), consider trayer or
 stalonetray.