I do not know how your nicad pack is made. That being said:
Most packs are made from individual rechargeable AA cells. The nicad cells often have a short life. They don't store well as a result of the high self discharge rate. They don't like to be overcharged and are easily damaged. You may be able to rebuild your existing pack yourself, or to get a hobbyist to assist you. A better choice of cell is the nickel-metal-hydride. (Nmh) The milliampere/hour (mah) rating on your pack will tell you the minimum specs for your replacement cell type. Nmh cells are much more rugged and are not plagued with the failure problems relating to nicad charge/discharge cycles.
The nominal terminal voltage of an nmh cell is 1.25 volts. If your pack is 12 volts, you will need 10 replacement cells. If you can carefully open your existing pack, you will be able to count the number of cells needed for the repair. Older nicad packs used 1200mah cells. Nmh cells come in a variety of storage ratings. You will be able to build your new pack using 1800mah or higher current ratings, which will give you a longer run time.
Good luck!
