According to the author, the HP 50G is an awesome calculator. But as awesome as it is, it is powered off of not-so-awesome AAA batteries. These little batteries don’t last long under the load of the calculators awesomeness, so a mod needed to be done. The battery chosen for installation was a replacement battery for a Sony PSP. He was able to find one, including the external charge regulator board for $10. Dropping it into the case and wiring it to charge off of the existing mini USB port looks fairly simple, very few actual modifications are necessary to the body. Unfortunately, they did end up with an LED protruding from the bottom that makes it wobble a bit, but they’re guessing that they get about 2x the battery life now.