And what you want displayed is the output of:
perhaps with some leading and/or trailing text.
I think that Amazon's gasgauge-info script already munges the percentage sign into the numeric string on all firmware versions,
If so, then
Code:
eips 1, 2 `gasgauge-info -c`
With changes in the x, y starting position of your choice should 'just work'.
Note: Those are back-ticks, not single quotes.
And since it is a single command, you don't need a bin/shell-script.sh to get it done, just put it as the 'action: ' in the menu.json of your new button.
(Unless the version-2 KUAL parser broke that feature. The version-2 parser is a bit annal in the things it will accept.)