Rechargeable batteries are not only expensive, but also are relatively short-lived! Whether a $35 cell phone battery or a $200 laptop battery, it makes sense not only to initially select the proper battery, but also to extend its life to the fullest extent possible. Let###s explore the types of batteries used in cell phones, laptops and camcorders and examine some criteria for selecting the proper type for your particular usage pattern. Finally we will look at some steps to prolong battery service life.
Portable devices such as cellular phones, laptop computers and camcorders use three different rechargeable battery chemistries, or battery types. These different types of batteries are sometimes interchangeable and like most things, all have good points and bad points. Unfortunately, the consumer often is not made aware of the whole story, since the marketing hype generally focuses on the advantages of each type without mentioning the disadvantages. For example, Nickel-Metal Hydride (NiMH) batteries are being touted as "memory free" and able to be "recharged without being fully discharged". This is the ###good### side of NiMH. We will discuss the ###bad### other side later.
There is really no one ideal battery type or chemistry which can be recommended, and in many cases the device does not offer a choice anyway. However, an informed buyer is able in many cases to make a battery selection which is better suited and offers better value than a purely random selection, which is what most of us are confronted with. We will attempt to inform on the selection criteria using a minimum of technical jargon.
The three popular battery types are nickel-cadmium (NiCd), nickel-metal hydride (NiMH) and the new Lithium-Ion (Li-Ion) chemistry. A few older cellular "bag" phones and older camcorders use lead-acid batteries, but this battery chemistry has not been incorporated into new electronic designs for a number of years.
The NiCd battery is the traditional favorite and is a good, long-lasting workhorse. Its useful life in a cell phone or laptop computer is usually between two and three years before noticeable degradation occurs. Of course, proper care must be taken to achieve this expected life and minimize the so-called "memory" effect. ###Proper care### means the NiCd battery should be fully discharged at each use, and should not be overcharged but should be taken off the charger at the first indication its charge is complete. NiCd batteries are also the most popular type used in camcorders and usually enjoy two to four years of life because of their less frequent use in this application.
NiCd batteries were the original type used in cell phones. However, the NiMH battery is rapidly replacing the NiCd battery in cellular and laptop applications. A major advantage of this battery chemistry is its higher capacity. NiMH batteries contain about 25% to 40% more energy in the same size battery as does a NiCd battery. Another advantage of a NiMH battery is the "memory free" characteristic, although as it approaches end-of-life it does develop a similar reduction in capacity. However, we now face the first "trade-off" in choosing between NiCd and NiMH batteries in a cellular phone application. This is the "down-side" of NiMH batteries that the marketing people do not mention in their brochures.
NiMH batteries, while being more "memory free" than NiCd have only half the useful life of a properly maintained NiCd battery. A NiMH battery will enjoy about twelve to fifteen months of service at full capacity in a cell phone or laptop; whereas a well-maintained NiCd battery should give twenty-four to thirty months of service. A NiMH battery also carries a higher cost than a NiCd, somewhere in the order of 25% to 50% more. A NiMH battery also tends to be more sensitive to overcharging than a NiCd battery. All batteries are damaged by overcharging, but NiMH even more so. Finally, a NiMH battery has twice the self-discharge characteristics of a NiCd battery. That is, a NiMH battery looses about 3%-4% of its energy each day when it is not being used while a NiCd loses only about half that amount.
Now, which type, NiCd or NiMH, makes the most sense for a cell phone? Why would one choose a NiMH battery over a NiCd battery? A heavy cell phone user who relies on the phone to conduct business and cannot afford to have the battery run out before the end of day is best served by a NiMH battery. He/she is interested in the longest talk/standby time possible and therefore needs the highest capacity battery available, which will be NiMH for most phones. This will also be the more expensive battery with a shorter life, but its selection is probably the best business decision. On the other hand, the cell phone user who keeps the phone in the glove compartment just for emergency use is probably best served with the least expensive NiCd battery that can be purchased. Not only is it less expensive, the higher capacity of NiMH is not needed, and the NiCd battery has a self-discharge rate of only 1% to 2% per day while setting unused. Other ###casual### cell phone users will also find NiCd batteries a better value, but for some, saving the aggravation of having to discharge the battery at each use is worth the premium price of a NiMH battery.
As a side note, when comparing battery prices always look at capacity versus price. And compare capacity in terms of the technically-definable milliamp-hour (mAH) rating, not talk or standby time, which are more subject to the whims and definitions of the marketing departments. The ###mAh### rating is usually printed on the label of the battery. Cost per milliamp-hour is the best way to compare battery value.
Selecting the proper battery for a camcorder is also quite dependent on the type of use. Camcorder batteries can be purchased to provide camera run times of 1, 1.5, 2 and 3 hours. We advise that the typical use pattern be considered before selecting a battery. For example, a family with infants or toddlers can easily be satisfied by a one-hour battery, since the antics and attention spans of the subjects are short-lived. Selecting a three-hour battery to take pictures of an infant means that either the battery should be run down for nearly three hours after a ten minute filming session, or the camera is put away and the battery is allowed to self discharge in storage. Either way, it defeats the purpose of an expensive, high capacity battery. A three-hour battery makes much more sense for a scenic vacation trip or for a visit to Disneyland or to film the sports activities of older children where its large capacity is a real advantage. Of course the variations between one hour and three hours allow the battery capacity to be ###tuned### to the most typical use of the owner.
Camcorder batteries with running times of two hours or less are NiCd batteries, while the high capacity three-hour batteries are NiMH. In the situation of a camcorder, the theoretically shorter life of NiMH is not a big factor, since a camcorder is generally used a few dozen times per year, not daily as is a cell phone or laptop. The "wear-out" factor with batteries is primarily the number of charge/discharge cycles, although ###age### eventually becomes a factor if the battery is seldom used.
The evolution of laptop batteries has followed the same pattern from NiCd to NiMH and now to Li-Ion. For the most part, a laptop user has little choice in the matter of batteries. A few laptops have batteries available in both NiCd or NiMH chemistries, but because of the different shapes and sizes of laptop batteries and the short life span of any given computer model, battery manufacturers have chosen not to make a variety available. Generally, if the laptop came with a NiCd battery, that is the only choice available.
Laptop batteries, though, require the same treatment as cell phone and camcorder batteries; full discharge at each use; no overcharging. If the laptop is used mostly on wall power, it is best to remove the battery so that it is not being constantly charged, as this has a deleterious effect on its life.
The newest battery chemistry, Lithium-Ion, is the latest and greatest according to the marketing people. Li-Ion has one very distinct advantage; it provides a much higher energy capacity in a given space than NiMH batteries, and of course than NiCd batteries. Thus, Li-Ion is the battery of choice among developers