What I did, is I created a custom font with BMfont, with just a few characters in it. And then modified the .png for those characters to become icons. I think many people do something like this.
Then to use them, I load the font, and then use that font to display the icons. (this way you can also change the color of icons without needing multiple bitmaps.
So for example,
dc.drawText(x,y,myiconfont,"B",Gfx.TEXT_JUSTIFTY_CENTER);
displays my battery full icon, while the same with "b", my battery empty icon.
I have tried this but when i try to run the watch in the simulator i get an OOM (out of memory). Also, do your edits to the .png file let you set which characters represent which icons? IE B = full and b = empty.