I would just Get Info on the App and paste a picture into the Icon well. It doesn't change the underlying icon, but puts a custom icon on top of it. Not sure how that would present when run.
For the Battery icon, just set the Finder to display the icon very large and take a screenshot. Cmd-ctrl-shift-4 will give you a selection marquee. Drag around the icon image to copy it to the clipboard. Paste into the Get Info icon well.
Otherwise, I don't know how to make it work.
I use a program called Platypus to bundle AppleScripts and Shell scripts into Apps. It allows you to set a custom icon.
You could just use an AppleScript for the entire thing, and use Platypus to "App"-itize it with your icon. The Full AppleScript is just:
set apcInfo to do shell script "apcaccess"
display dialog apcInfo as text buttons {"Ok"} default button "Ok"
Oops, I didn't see that BDAqua already suggested pasting an image on the icon.