After eating through many blister packs of D cell batteries from the store, our baby swing was getting quite expensive. I thought it was time to replace those expensive batteries with some 18650 Li-ion cells that could be easily recharged. I knew the batteries had enough horsepower to run the swing, but I had a small problem. What was my problem, you ask? The cells were unprotected. I could have ordered some protection circuits from China through the wonderful world of eBay, but I wanted to have my protection circuit sooner than next month. My solution? Use a microcontroller to monitor the voltage on the battery, and then turn off a MOSFET when the battery dipped too low. I always have a few Arduino Pros lying around for the miscellaneous project, so that was the obvious choice for the project. (Or at least for the prototype. I wasn't sure if the power consumption would be "low enough") To drive the MOSFET I built a Dickson charge pump to produce the necessary voltage from the battery voltage. I then realized that instead of adding additional circuitry to turn the MOSFET on and off, I could just turn the charge pump on and off to control the MOSFET. This reduced complexity significantly and reduced the parts count. The final result? My son loves his working swing, and I love the money I'm going to save!