Many of the devices that are in use today are powered by rechargeable battery packs. Although these battery packs are rechargeable, if they are put into heavy use and undergo one or more charge and discharge, they will eventually begin to fail. Replacing a battery pack can sometimes be prohibitively expensive, especially when you consider it versus the cost of replacing the entire device. In this situation, you may consider making a homemade battery pack. This process can also be used to create battery packs for custom applications.
Decide upon the voltage for your battery pack. Do this by looking at the pack you are replacing, or by considering the needs of your custom application. Buy enough rechargeable cells so that their individual voltages will add up to that which you require. Rechargeable cells usually have a voltage of 1.2 volts, and are available in standard AAA, AA, and C sizes. For example, if you need a 14.4 volt pack, you will need 12 individual cells. The larger the physical size of the battery, the greater the battery capacity, so also consider this as you determine the size of your pack.
Arrange the cells you have purchased to the planned shape of the battery pack you are building. You may stack them, stagger them, and place them in whatever arrangement fits your needs.
Use the spot welder to attach nickel strips between each cell so that the positive contact of each cell is connected to the negative contact of another. You must connect the cells in this way so that the voltage of each cell is combined.
Spot weld the positive and negative leads from the device you are powering with the pack to the respective contacts on one of the cells. For example, weld the positive lead to the positive contact on one of the cells, and the negative lead from the device to the negative contact on the same cell.
Place all of the cells into a piece of shrink wrap tubing that has been cut and trimmed to fit your pack. Heat the wrap until it shrinks down snug over the cells, and you are finished.