Without getting too deep into the details of electricity you can measure these things:
- Voltage. One volt means how much pressure required to push one amp of current against one ohm of resistance. In electrical terms, here is the amperage.
- Wattage. This number tells you the total amount of work you can do with the battery. Multiplying voltage times amperage calculates wattage.
At home or office, your electric company calculates your bill based on kilowatts per hour, which is a measurement roughly equivalent to using 1,000 watts of power for an hour. (For example, in perfect conditions a 100- watt light bulb burning for 10 hours consumes 1 kilowatt.)
Laptop computers use power in smaller quantities, typically demanding somewhere between 35 and 75 watts of peak draw. (Peak draw might occur in this situation: The LCD is fully lit, the graphics adapter is hard at work producing constantly changing, complex images derived from a DVD, a whole bunch of RAM is being powered, the hard drive is spinning, and the WiFi adapter is switched on.)
Battery wattage or amperage
With regards to the bucket of power called a battery, we're not quite at the stage where a small, lightweight laptop can acquire a kilowatt or more of stored power. Instead, we talk about watt hours or sometimes amp hours.
One watt hour (WHr) is the amount of electric energy required to power a 1- watt load for an hour. A laptop that draws typically 20 watts per hour runs for about two hours on a fully charged battery rated at 40 WHr. A way to rate a battery is to express its capacity in amp hours (AH). Amp hours are like the explosive potential of a tank of gas, while watt hours represent the distance that power can drive the car. To convert watts to amps, use this formula:
watts / volts = amps
You may see amp hours expressed like this: 4.4 AH. Or some techie may prefer to rate the same battery as 4400 mAH. (An mAH is a milliamp hour, and 4,400 milliamps is the same as 4.4 AH.)
Batteries offered today usually range in capacity from about 25 WHr up to 96 WHr. An ordinary range of amp hours for laptop batteries is from about 4 to 8. In terms of choosing a battery, watt hours or amp hours are really the only number (other than the weight) to which you should pay attention. A larger capacity is better than a smaller bucket of juice ... but also heavier.
Battery weight
The more watt hours a battery produces or amp hours it contains, the longer the laptop can operate. You'd think, then, that the solution was oh- sosimple: Get as many as you can. The problem is that batteries require metals and chemicals to hold a charge, and the greater the capacity, the heavier the device.
Breeding hybrids
Scientists are hard at work developing new hybrid metals and electrolytes (literally, the juice within the battery) that can hold more power without turning into an electronic cinder block. The current champion at least for consumer- grade products is Lithium Ion (LiOn) technology. Other designs in the labs include polymer- based alkaline, lithium nickel manganese oxide, lithium cobalt oxide, and Spam in a Can. Okay, I made that last one up, although it probably could generate gas some way.
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08192010
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