I recently purchased an ultra-cheap dremel-like wireless rotary tool. Of course I got what I paid for, because the battery packs (two were surprisingly included) are low capacity, short running pieces of ni-cad crap. After a full charge you could only expect 10 mins of runtime! I figured I would just have to replace it. Then I found an old AC wall adapter that matched the power specs of the battery and thought about simply opening up the drill and soldering the leads directly into where the battery connects, but after looking at the 2 battery packs I decided to sacrifice one pack for its case to use as a removable plug for the wall adapter. With this setup, it now has the ability to be both wired and wireless. See the pictures and descriptions below. chances are, you could do the same thing with your particular brand of rotary tool. A WORD OF CAUTION: Please make sure the wall adapter you plan on using can provide enough amperage for your drill. If you are not sure what I mean by that, then don't do this project. You'll want to periodically check the adapter to make sure it's not overheating. When you're done using it unplug it from the wall!
Above is the drill, and disassembled battery pack before the simple modification.
Above is a detail of the empty battery case. You can see where the terminals need to be. I was able to clip the battery terminals off the pack so I could solder them to the wall adapter leads. I used a piece of styrofoam shaped like the old pack so the leads would fit snug inside the case.
Above is a picture of the "plug" that allows me to switch between wired and wireless power. Notice my bandaged finger-Be careful of disassembling the batteries!
