No, your eyes do not deceive you. That’s a wrist-mounted PDA. Specifically, a Fossil Wrist PDA, also known as an Abacus, that was sold from 2003 to about 2005. Yep, it’s running PalmOS. [mclien] has had this watch/PDA for a while now, and found the original 180mAh battery wasn’t cutting it anymore. He made a little modification to the watch to get a 650mAh battery in this PDA by molding a new back for it.

The original PDA used a round Lithium cell, but being ten years old, the battery technology in this smart watch is showing its years. [mclien] found two batteries (380mAh and 270mAh) that fit almost perfectly inside the battery.

The new batteries were about 3mm too thick for the existing case back, so [mclien] began by taking the old case, adding a few bits of aluminum and resin, and making a positive for a mold. Two or three layers of glass twill cloth were used to form the mold, resined up, and vacuum bagged.

After many, many attempts, [mclien] just about has the case back for this old smartwatch complete. The project build logs are actually a great read, showing exactly what doesn’t work, and are a great example of using hackaday.io as a build log, instead of just project presentation.