RECHARGEABLE BATTERIES July 28, 1996 *** NICKEL CADMIUM BATTERY *** The most common type of rechargeable battery is the nickel cadmium battery. It is called a Nicad battery. A Nicad battery can be charged and discharged hundreds of times. C CELLS: Most nicad batteries used in cordless drills and other cordless tools are smaller than a C cell. They are called sub C cells. The ordinary C cell Nicad you buy at the store contains a sub C cell. The rest is plastic. That is why it is so light. A Nicad built this way holds about 650 milliamp hours. Nicad batteries are available which are all battery and no plastic. They are call high capacity Nicads. A high capacity Nicad C cell can hold 1800 milliamp hours. That is almost 3 times more! D CELLS: Most D cell Nicads your find at the store cost the same as a C cell Nicad. Now why would a battery which is much larger cost the same as the smaller one? Because a D cell Nicad contains a sub C cell inside it. The rest is a plastic case and air spaces. It is very light. But it still holds only 650 milliamp hours of energy. There are available high capacity Nicad D cells. They can hold 4400 milliamp hours of electricity. That is 4.4 amp hours! Quite a lot. 4400 milliamp hours is 7 times as much as 650 milliamp hours. 9 VOLT BATTERIES: The ordinary 9 volt Nicad batteries you buy at the store have a voltage lower than the 9 volt rating. A 9 volt size Nicad battery is really only 7.2 volts. There are available 9 volt size Nicad batteries with an extra plate in the battery. The voltage is close to 9 volts when in use. These are called true 9 volt Nicad batteries. You may find that a ordinary 9 volt Nicad will not work in some applications. And you had to go back to expensive alkaline batteries. But the true 9 volt Nicad will work in these sensative applications. A good example is a smoke detector. It chirps when the battery is low. It chirps every couple of months with an ordinary 7.2 volt Nicad. But with a true 9 volt Nicad, it will last half a year before chirping. Nicad batteries are more expensive than alkaline batteries. But they can be recharged over and over. If you replace the battery in your smoke detector every six months, that is two a year. The Nicad will pay for itself in two or three years. That is a 33 percent or 50 percent return on investment. That is a great interest rate! MEMORY EFFECT: A Nicad battery remembers its past charge and discharge history. This is a problem with camcorder batteries. You must totally discharge a camcorder battery before charging it again. If you recharge a partly used battery, you will only be able to use the camcorder a short while. *** RENEWAL - RECHARGABLE ALKALINES *** These are better than ordinary alkaline batteries since they can be used over and over. But you can only recharge them 25 times. They also loose a little capacity each time so by the 25th charge the capacity is down to 1/2. Alkaline rechargeable batteries have a normal voltage of 1.5 volts. This makes them good for electronic devices such as digital cameras. *** NICKEL METAL HYDRIDE BATTERY *** There is a new type of rechargeable battery available. Nickel metal hydride batteries are called NiMh batteries for short. ADVANTAGES: Nickel metal hydride batteries have two or three times the storage capacity of Nicads. A Nicad AA cell holds 300 to 500 milliamp hours. A NiMh AA cell holds 1200 milliamp hours. That is 1.2 amp hours - quite a bit more than the NiCad! NiMh batteries have no memory of past use. You may partially discharge a NiMh battery and then charge it up full. NiMh batteries are environmentally friendly. NiMh batteries can be disposed of in ordanary household trash. DISADVANTAGES: You must charge a NiMh overnight. No quick charging. *** LITHIUM ION *** The newest type of rechargable battery is the lithium ion battery. They are light and hold a lot of energy per ounce. They are used mostly in laptop computers since they are still rather expensive.