YOUR GUIDE TO LAPTOP BATTERIES AND CHARGERS
TYPES, CHARACTERISTICS, REVIEWS
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Technically
speaking, a battery
is an electrochemical device that converts stored chemical energy into
electrical energy. When connected to an electric load it can produce an
electric current. Batteries are used in a wide variety of applications,
such as small hand-held devices and home power backup systems. Under
normal conditions when AC power is present, the AC-DC adapter (laptop power supply)
maintains the laptop battery charge and provides power to the circuits.
The charged battery powers the circuits when DC voltage from the
adapter is not available. There are three different battery types for laptops: NiCd, NiMH and Li-Ion. Nickel-Cadmium (NiCd)batteries were the original type. They could supply power for about two hours between charges, suffered from the memory effect and could explode when overcharged.Nickel-Metal Hydride (NiMH)batteries represent the second generation of the energy storage. They generally have 10-25% greater capacity than NiCds, are environmentally friendlier, but still suffer from the memory effect, although to a lesser degree.In both types of Nickel-based batteries crystals build up occurs over time that prevents you from charging them completely and would require full discharge to restore the capacity. Lithium Ion (Li-Ion)batteries currently are the latest energy storage technology. Li-Ion's are used in a broad range of devices including hybrid vehicles. They can deliver typically 40% more capacity than comparable NiCd packs, are lighter and thinner, have low self-discharge and better cycle life, do not suffer from memory effect, and normally won't explode if overcharged (although there were cases when they did explode when overheated). Newer Li-ion phosphate cells are inherently safer.Standard LiIon batteries for notebooks may have up to 3-6 hours run time with the life from 400 to 1200 charge cycles. They are also more convenient since they do not need full charges and discharges for peak performance. A typical charger provides fast charge to 80% Li-Ion pack capacity, then switches to trickle charging for another two hours to fully charge. There is a modification of a Li Ion cell called Li-Ion polymer. The difference between these two types is in the latter a solid ion conductive polymer replaced the liquid electrolyte. A Li Ion pack consists of a number of the series/parallel connected cells (typically from 4 to 16) to provide the required operating voltage and current levels. Nominal voltage of each cell is typically 3.6-3.7 V, the charging voltage is about 4.2-4.3 V per cell. The Li-ion phosphate cells have 2.9V nominal and 3.6V charging voltage. Note that because of the cell's relatively high voltage, many low-power portable products can operate from a single cell. Depending on the cell connection scheme, the nominal Lithium Ion battery voltage for a laptop computer can vary from 7.2 V to 14.8 V (typical voltages for major brands are: 11.1 to 14.8 V for Dell laptops, 10.8 to 14.8 V for Toshiba, Apple, Gateway and IBM laptops, 7.4 to 14.8 V for Sony, 7.2 to 14.8 V for HP, 14.4-14.8 V for Compaq). Note that the output voltage rating of a laptop power supply is not necessarily the same as nominal battery voltage. Over time any battery looses its capacity whether or not it is being used. For longest battery life, Li-Ion packs should be stored at their nominal voltage (3.6 V per cell) at about 40°F. The fastest permanent capacity loss occurs at elevated temperatures with the pack maintained around 4.2 V per cell (which is fully charged). In most cases the packs are actually used in the worst conditions: they are inside a laptop that drives them hot are usually connected to the charger that is keeping them fully charged all the time. The more time the cell remains at high float voltage, the shorter its lifetime. On the other hand, frequent full discharges should also be avoided when possible. To increase the battery life try to use partial-discharge and partial-charge cycles instead of keeping it always fully charged or going through full discharge and full charge cycles. Any system may eventually require a replacement battery. Consider replacing it when you notice substantial decrease in its run time. If you can't get the exact part number, a substitute with a slight VDC difference is usually OK since the pack's volts normally vary by 15% depending on its charge level and the load. However, it is always advised to check with your brand's manufacturer. To boost the running time by 4 to 10 hours you may use a universal external laptop battery 
from a third-party manufacturer.The resources below provide an additional information. |
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LAPTOP POWER SUPPLY AND
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RESOURCES FOR HOBBYISTS |
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CNET's guide to laptop computer batteries How to prolong lithium-based product life |
How to rebuild a LiIon battery pack A method for minimizing notebook adapter power rating and battery charging time for Li-Ion battery pack Toshiba laptop battery replacement- Illustrated how to repair the pack Fixing laptop power supply |
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