This project was created to help with pet nails. We had a full family of dogs (3 total) and all of them had healthy nails that needed constant care. We went through all kinds of batteries to keep the nail trimmer going at a good speed, and that was getting costly, and rechargeable batteries were not going to be the answer because of the current pull being so high.
I took the PediPaws apart to see what I was working with, and it was a simple on/off switch and motor. The batteries were in series, so I knew that the voltage for everything was only 3V DC. I soldered some leads to the switch and put a barrel jack on the bottom, then used a standard Radio Shack variable power supply that ranged from the 3V - 12V to power it. I was able to use the power supply for other projects, but ended up keeping it with the animals stuff for ease of use.
I bumped up the voltage from 3V to 5V to see if that would make the trimming time shorter, and that made the cutting head to act erratic and removed to much nail while trimming. The battery output @ 3V is the correct voltage to get everything working perfectly. If you want to build a voltage divider or use a regulator to get the 3V could work too, but I didn't mind sharing the power supply.