It is quite easy to convert an "AA" battery into either a "C" or "D" sized battery. What is not commonly known is that "C" and "D" batteries are essentially identical to their "AA" counterparts (i.e., same height, etc.). What differs is the diameter of the cylinder that contains the metal and chemical which makes the battery function. Basically, the makeup of the batteries are same, but the case size is different.
The following steps will demonstrate how to resize a "AA" battery-which are less expensive and more efficient-to a "C" or "D" size. The process won't take long to complete because it doesn't involve any internal function of the battery.
Step 1 - Measure the Batteries and Cardboard
Measure the exact height of the "C" or "D" battery’s external shell. Do not include the round protrusion on top that is the terminal. Only measure the height from the widest point on the bottom to the widest point on the top. Measure and mark the cardboard to the identical height.
Step 2 - Cut Out the Cardboard
Use the scissors to cut out the cardboard, making sure to keep it the exact height of the battery. Cut it to a length of about 12 inches. The resulting cardboard rectangle should be the height of the battery by 12 inches (H x L).
Note: The length of the strip will need to be longer to convert a "AA" battery into a "D" size due to its larger size.
Step 3 - Affix the Cardboard
Lay the "AA" battery on one end of the cardboard strip.
Make sure that the top and bottom of the battery (not including the terminal) are lined up exactly with the edges on the short end of the cardboard strip.
Apply two or three pieces of Scotch tape to fasten the end of the strip to the battery.
Step 4 - Roll the Cardboard
Carefully roll the cardboard strip around the battery, making sure that the edges of the cardboard stay level with the battery. Wrap it around tightly.
When you come to the end of the cardboard, fasten it with another two or three pieces of tape.
Step 5 - Insert Battery
Test out your makeshift "C" or "D" battery by inserting it into a device that uses one of those types. The cardboard padding gives the "AA" battery a wider diameter so it will fit into a "C" or "D" battery slot. The terminals should still touch the metal spring and clip on the device. If the battery wobbles around, it may not have enough cardboard attached to effectively increase its size. If that is the case, start over with a longer piece of cardboard.
This conversion is simple because all you need to do is increase the diameter of the smaller battery to fit into a device that needs the larger battery compartment. The internal functions are identical. Once you perfect this method, you won’t ever have to buy C or D batteries again.