Check the input voltage requirement of the device you want to convert from battery to transformer power. It’s important you use a transformer that produces the same voltage as your electrical device, or you may damage it. You can find the voltage on the label of your electrical device.

Purchase a transformer from an electrical store. They are widely available, inexpensive and you can get one that produces the same voltage as your electrical device, or one that has variable settings so you can use the transformer to power several different devices. Buy one with screw terminal fittings so you can easily wire between the transformer and your electrical device.

Remove the battery cover from your electrical device. Either unclip it using your fingers, or if it’s held in place using screws, use a screwdriver to remove the screws then lift off the cover. Remove the batteries from your device so you can access the terminals inside the battery holder. Pry them out using your fingers, or insert a small screwdriver at one end and lever out the batteries.

Cut a strip of dual-core AWG 16 gauge wire using a knife. Cut it the length required between your transformer and electrical device so you can move the device around a little.

Use wire strippers to remove 3 inches of the outer plastic covering off the ends of the dual core wire so you can see the two internal wires. The wires are usually red and black, but this can vary. The important thing is you have two different colored wires so you can correctly connect positive to positive and negative to negative. Remove 1/2-inch of colored plastic off the ends of the wires using wire strippers.

Loosen the terminal screws on the transformer. Some terminals have knurled screws so use your fingers to loosen them; others need to be loosened using a screwdriver.

Insert one of the colored wires under the transformer’s terminal screw labeled “+” or “Pos,” then tighten the screw using your fingers or a screwdriver so it's held securely in place. Note the color of the wire since you need to connect the opposite end to the positive terminal on your electrical device.

Insert the other colored wire under the terminal screw labeled ''-" or "Neg" and then tighten the screw as before. Make sure both connections are tight and secure.

Drill a small hole near one of the corners of the electrical device’s battery cover using a hand or power drill. The drill size needs to be slightly larger than the size of the dual-core wire, so measure the diameter of the wire using a ruler.

Insert the dual-core wire through the hole in the top of the battery cover. Push enough wire through so you can connect to the battery terminals.

Locate the positive and negative terminals in the battery container of your electrical device. They are labeled the same as the transformer terminals: "+" or "Pos" and "-" or "Neg."

Attach the opposite end of the colored wire that’s attached to the positive terminal on the transformer onto the positive terminal of the battery terminal. Use a strip of tape to hold it in place. Attach the opposite end of the colored wire that’s attached to the negative terminal of the transformer to the negative terminal of the battery terminal using the same method.

Replace the battery cover by clipping it in place using your fingers or replace the screws and use a screwdriver to tighten them. Insert the plug on the end of the wire from the transformer into the plug socket. Set your transformer to the desired voltage, if it has variable settings, then turn on the transformer. If it doesn’t have variable settings, simply turn on the transformer. Your electrical device now operates using the transformer rather than the batteries.