Another popular battery hack involves the A23 12 volt battery. These are often hacked as a cheap source for button cell batteries. To do this hack, take a pair of needle nose pliers and pry up the top corner of the seam in the metal casing. Then peel away the metal casing and remove the cardboard insulation. Inside will be eight LR932 button cell batteries. These button cells are a fairly popular size and can be used to power a wide variety of small electronics. The main advantage of this hack is that these button cells are usually much cheaper than buying them from the store directly. This is really useful because button cell batteries are used in a lot of hacking projects. For example they are great for making LED "Throwies" But my favorite application is making miniature battery packs. If you ever want to miniaturize a circuit project, the first thing to do is use smaller batteries. Here is a quick example showing how you can make a miniature 9 volt battery.
First make a stack of 6 cells and wrap them in tape to hold them together. Then cut a piece of heat shrink tubing that is about an inch longer than the batteries. Insert them into the tubing and shrink the tubing starting at the ends alternating from one side to the other and back. This will squeeze the batteries tightly together and help make a good connection. Use a sharp knife to trim off any excess tubing so that the tubing is flush with the end of the batteries. Use a voltmeter to check the voltage. Fully charged this battery pack should read out at a little over nine volts. Now you have a 9 volt battery that is less then ¼ the size of a standard 9 volt. This can go a long way in making miniature circuits. The only down side is that this battery pack will only have capacity of about 55mAh instead of the 565mAh in a standard 9 volt battery.