Come to think of it, the "copper top" is a fun example; think of the use of the phrase in The Matrix. Also common slang for a redheaded person in parts of the US. There's an argument that "copper" and black helps get across the "battery" meaning of a tiny icon. Is Duracell in danger of losing control of its trade dress? :-)
Cheers, - Michael P. S. In a laptop battery monitoring app, I would give the battery a black outline and denote the charge level with, say, blue (above about 1/3 full) or red (under 1/3). And then mention color-blindness in the docs to say that the colors are chosen on purely functional grounds. Otherwise you're almost certain to duplicate somebody's trade dress. Then again, you could live dangerously and change it from Duracell to Brand X after determining that it doesn't report its charge level reliably. :)
