I know it's an old
thread, but others may still find it useful.
I highly recommend Drozd's method with sanding sponges. Haven't tried it on an eGo, but my 4081 batts sure looked spiffy once upon a time. Start at 150 grit to remove the paint. Then go with progressively finer sponges to remove the tiny scratches. I finish off with 0000 steel wool for a look that is almost "chromed." Be very careful though, if the wool catches it will spool up on the battery tightly and could wrench itself out of your hands... or worse, injure you. Alternatively, the drill technique does leave behind a nice brushed finish with sponges alone.
Another idea I just thought of is sanding film. You can usually find it in the paint section of an auto parts store or a hobby
shop that caters to modelers. I've seen film as fine as 600 grit.