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Battery Best Practice Guide: Lithium Ion, Nickel Cadmium, Nickel Metal HydrideCESD|200058Applies To
OverviewHandheld PC devices have evolved along with battery technology. Original generation Handheld PC 1.0 devices made use of standard Nickel Cadmium cells. As devices evolved so did the use of battery technology. First to Nickel Metal Hydride and finally onto device specific and highly customised Lithium Ion cell packs. This article discusses the best practises for maintaining, using, charging, storing and disposing the main battery cells in your device. GuideThere are three types of main cell that different Handheld PC devices may operate with. Most devices newer than 1998 will make use of customised battery packs. Devices newer than 1999 will usually only use Lithium Ion cells. Which chemical type does my device use?To ascertain this you will need to look at the battery compartment's rating plate or your Handheld PC's manual.
Nickel Cadmium / Nickel Metal HydrideCadmium and Metal Hydride batteries are not commonly found in newer devices as they cannot provide the sustained current provided. For older devices, especially ones with Monochrome display's their use is common. Your Handheld PC may come with a custom sized battery or use standard size battery's such as AA. Nickel Cadmium is the oldest of the rechargeable technologies discussed here. It is also by far the cheapest and the most unreliable. Measured in Milliamp-hours (mAh), which specifies the storage capacity of the battery. The higher the mAh the longer the battery will last. The usual delivery by a NiCd or NiMH cell is 1.2 volts. Cadmium cells will rapidly self drain, often in as little as a month or less. Generally the discharge rate is 1 - 5% of total capacity per 24 hour period. This is irrespective of whether or not they are present in the Handheld PC. Cadmium batteries are also seriously affected by environmental conditions, most notably by the ambient operating temperature. Storage When you wish to store a Nickel based cell or your device for a prolonged period of time you should ensure that it is kept away from direct sunlight, in low humidity and as cold as possible (down to refrigerator temperature at most, never freeze them). 15 degrees Celsius is optimal. There will always be a loss of capacity when storing your batteries. Charging NiCd cells will rapidly suffer a capacity drain if not maintained vigorously. This drain, sometimes referred to as the "Memory Effect" is caused when the cell isn't completely discharged before it is given a complete charge cycle. You should purchase a special management charger which will discharge the battery before charging it up. NiMH cells do not suffer from the Memory Effect to the extent of NiCd, however the use of a discharger is strongly recommended. We recommend that you do not use the charging facility on your Handheld PC device unless the battery is non-standard. For Standard AA cells we strongly recommend that you purchase a special charger and perform all charge / discharge operations using that. When removing after an extended period of storage you should provide a 24 hour trickle charge. If the battery has been stored for longer than 6 months you should perform a priming operation on the battery. This involves performing a slow 24-hour charge followed by at least one (preferably more) fast discharges / charges. Disposal Nickel based Cells contain extremely toxic chemicals and can be environmentally devastating. Never attempt to heat, incinerate, crush or dismantle your battery. You should make use of proper disposal services within your local community. Lithium Ion (Li)Lithium Ion is one of the newer battery technologies on the consumer market, and is the most common found in Handheld PC devices. It is also the most expensive. Lithium Ion batteries (not to be confused with single use Lithium) are incredibly light compared to other kinds of battery. Making them ideal for use in portable consumer devices. Lithium Ion has a high energy density which means for the overall physical size and weight they can store more energy than other types of rechargeable cell. By default a Lithium Ion battery operates at a much higher voltage than other conventional technologies. This allows for more power from less cells and there for significantly impacts the design of a particular device. Typically a Lithium Ion cell operates at around 3.7 volts, where as a NiMH or NiCd cell can only provide 1.2 volts. Lithium Ion cells like all batteries suffers from self discharge. With Li however it is significantly less than NiMH or NiCd. Usually able to hold charge for several months with no active use. Storage When you wish to store a Li cell or your device for a prolonged period of time you should ensure that it is kept away from direct sunlight, in low humidity and as cold as possible (down to refrigerator temperature at most, never freeze them). 15 degrees Celsius is optimal. Lithium batteries can be stored for up to 10 years as long as they are given monthly top-up charges. Charging Lithium-Ion cells use a microchip to maintain a very delicately balanced charge rate. If you have any reason to believe that the battery has sustained shock or damage that could in any way affect the circuitry you should dispose of the battery immediately. Lithium-Ion battery's prefer incremental (top-up) charges rather than complete discharges preferred by other battery technologies. We recommend that you fully discharge the battery as little as possible. No more than one fast discharge / charge every year is recommended. For all other general use incremental charging should be applied with power levels not being allowed to fall below 20% of capacity. In an effort to preserve the usable life of a Lithium-Ion batery, you should avoid fully charging the battery. To preserve the optimal life of the cells you should attemot to keep the charge level at between 40% and 80%. Charging from under 40% places extra stress on the battery cells and can cause memory issues. Charging from 80% up to 100% places significant strain on the battery, requiring additional energy to force power into the cell. This extra energy creates additional heat that further undermines the general health of the batteries. You should not leave a Lithium-Ion cell on charge longer than necessary. On most appliances, once the desired charge level has been achieved, you should disconect the charger. Some more advanced charge controllers are desined to manage the charge rate and compliment it with a discarge and managemenent cycle which allows the device to be left on charge permanently. Most cosumer devices such as PDA's do not have this type of charge controller and consequently you may prematurely degrade your battery through overcharging. This may cause the battery pack to physically swell in size, damaging the device and - over an extended period - could present a fire risk. Priming (Performing a slow charge, followed by several fast charge / discharge's) Li cells after prolonged storage is not necessarily required. As Lithium-Ion best practice dictates you should not fully discharge Li cells and repeated use of priming should be avoided. Disposal Lithium Ion batteries are fully recyclable and should be disposed of using an appropriate system (Such as a special recycling centre or via your local government waste disposal centre - European Union law requires local government provide facilities for disposal of such items). You can also return them directly to some OEM's for recycling. |
