I have 3 batteries for my powerbook that i switch in and out. They tend to get confused at meeting points for mac users such as conferences so I thought I'd label them via laser etching.
Step 1: Select a file or image for marking the back of the battery.
Step 2: Place in laser-etcher's bed. eg: the Epilog i have in my shop.
i referenced it to the top corner and used the alignment features in Corel to make sure it was in the right spot.