Mar 16, 2008

Crave for power? Protect your Li-ion battery

Nokia Li-ion Battery Almost all modern electronic gadgets come with batteries. Right from your notebook computer to a mobile phone, a digital camera to an iPod -- all derive their power from a battery. This makes our digital lives so very dependent on these power-packed devices.

How many times have you gone out shopping for a new battery for one of your devices hoping for a longer backup time, only to see it fall short of your expectations within a few months of use?

Welcome to the club. Almost all of us have faced this situation one time or the other. Whether it is a mobile phone or a laptop, I have almost found myself cursing the battery manufacturers for screwing our lives so royally. After 6 to 12 months of constant use, the life of the battery falls down to such pathetic levels, that continuing to use them any more becomes a nightmare. Eventually they need to be replaced.

image Lately I started wondering what is the root cause of this problem and if there is a way I can try to prolong the life of my Lithiom-ion batteries. As it turned out, there is a way. To understand that, you first have to know a little bit of technical detail of how a Lithium-ion battery works.

Lithium-ion batteries (sometimes abbreviated Li-ion batteries) are a type of rechargeable battery in which a lithium ion moves between the anode and cathode. The lithium ion moves from the anode to the cathode during discharge and from the cathode to the anode when charging.

Lithium ion batteries are currently one of the most popular types of battery for portable electronics, with one of the best energy-to-weight ratios, no memory effect, and a slow loss of charge when not in use. Certain kinds of mistreatment may cause Li-ion batteries to explode. Although originally intended for consumer electronics, lithium-ion batteries are growing in popularity for defense, automotive, and aerospace applications due to their high energy density.

image Lithium-ion batteries can be formed into a wide variety of shapes and sizes so as to efficiently fill available space in the devices they power. Li-ion batteries are lighter than other equivalent secondary batteries—often much lighter. Li-ion batteries do not suffer from the memory effect. They also have a low self-discharge rate of approximately 5% per month, compared with over 30% per month in common nickel metal hydride batteries.

However, despite all the advantages outlined above, the Li-ion batteries also have quite a lot of disadvantages. A unique drawback of the Li-ion battery is that its life span is dependent upon aging from time of manufacturing (shelf life) regardless of whether it was charged, and not just on the number of charge/discharge cycles. Under certain temperature conditions, the batteries have a tendency to become damaged and can sometimes never fully recharge again. As batteries age, their internal resistance rises. This causes the voltage at the terminals to drop under load, reducing the maximum current that can be drawn from them. Eventually they reach a point at which the battery can no longer operate the equipment it is installed in for an adequate period.

image Li-ion batteries can even go into a state that is known as deep discharge. At this point, the battery may take a very long time to recharge. For example, a laptop battery that normally charges fully in 3 hours may take up to 42 hours to recharge. Or the deep discharge state may be so severe that the battery will never come back to life. Deep discharging only takes place when products with rechargeable batteries are left unused for extended periods of time (often 2 or more years) or when they are fully discharged so often that they can no longer hold a charge. This makes Li-ion batteries unsuitable for back-up applications where they may become completely discharged.

imageA stand-alone Li-ion cell must never be discharged below a certain voltage to avoid irreversible damage. Therefore all Li-ion battery systems are equipped with a circuit that shuts down the system when the battery is discharged below the predefined threshold. It should thus be impossible to "deep discharge" the battery in a properly designed system during normal use. This is also one of the reasons Li-ion cells are rarely sold as such to consumers, but only as finished batteries designed to fit a particular system.

Given that Liuim ion batteries have so many problems, there are a few guidelines that you can follow to prolong the life of your batteries. Some of these guidelines might be too impractical to follow in everyday life, but they still serve as an advisory towards some practices that are a complete no-no for Li-ion battery users.

  1. Unlike Ni-Cd batteries, lithium-ion batteries should be charged early and often. However, if they are not used for a long time, they should be brought to a charge level of around 40% - 60%. Lithium-ion batteries should not be frequently fully discharged and recharged ("deep-cycled") like Ni-Cd batteries, but this is necessary after about every 30th recharge to recalibrate any external electronic "fuel gauge" (e.g. State Of Charge meter). This prevents the fuel gauge from showing an incorrect battery charge.
  2. Lithium-ion batteries should never be depleted to below their minimum voltage, 2.4v to 3.0v per cell. Most of your devices will handle this automatically. Even the finished batteries that you buy from authentic dealers will have an internal cutoff to prevent a complete discharge.
  3. imageLi-ion batteries should be kept cool. Ideally they are stored in a refrigerator. Aging will take its toll much faster at high temperatures. The high temperatures found in cars cause lithium-ion batteries to degrade rapidly. However, do not freeze the batteries.
  4. Li-ion batteries should be bought only when needed, because the aging process begins as soon as the battery is manufactured.
  5. When using a notebook computer running from fixed line power over extended periods, the battery should be removed, and stored in a cool place so that it is not affected by the heat produced by the computer.
  6. There is some benefits to fully discharging your lithium battery periodically, for laptops this can be especially important. If you start to notice your battery meter is becoming more and more inaccurate, it may be time for some battery calibration. By allowing your lithium battery to fully drain, this will help the battery recalibrate allowing for more accurate measurements of battery life. This should be done once every 30 charges or when you notice battery readings are off.

imageFollowing even some of these recommendations will help you derive the longest possible life out of your batteries and also help you save some money to spend on buying the latest new electronic gadgets.


Anonymous said...

Hi Nice Blog .I've made up my mind: I'm gonna buy an MP3 player. I just don't know which one. I like the ipod replacement battery, but do I really need something that small?

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