During their working life, rechargeable batteries in a laptop are repeatedly re-charged after they have been drained. The charging is accomplished by applying externally supplied electrical current through an adopter. The electrical current enters in the battery and reverses the chemical process which occur in the battery while it is in use. Devices to supply the appropriate current are called battery chargers.
Most of today's laptop computers are powered with lithium-ion batteries. Rechargeable laptop batteries have a tendency to self-discharge. This means they discharge even while not in active use. This self-discharging process accelerates at higher temparatures. It is not advisable to leave them unused for long time, due to their poor shelf life.
Under good conditions, a typical lithium ion battery can supply around 500 discharge/charge cycles, which is equivalent to 2 to 3 years of service, from the time the battery goes through the production process. As a battery is put into regular use, capacity loss occurs as a result of increased internal resistance caused by cell oxidation. Eventually, the resistance becomes so high that the battery can no longer deliver the needed energy to the laptop, even though the energy is still present in the battery. This usually marks the end of the useful life of a battery. It is believed that there are no remedies to restore the battery capacity when it is worn out. Heating the battery will improve its performance only momentarily and can not be considered a long term solution.
There are many free utilities available on Internet and from software developers that help in the testing of battery status. A typical utility constantly revises its estimate of remaining battery life, by measuring the time it takes to run it down. Such utilities are particularly useful when batteries read 100 percent when fully charged, but only run a few minutes before they run out completely. A power center would accurately show a 100 percent charge but it would also show about 5 minutes of time left.
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