CELL SUTRA

Battery experts say their biggest problem is heat. Too much warmth causes the battery to drain faster. John Wozniak, a technologist at Hewlett-Packard responsible for testing batteries, has some advice for the owner of a battery-powered device: 8220;You don8217;t want to leave it sitting on the front seat of a car. It8217;s like the care and feeding of the baby. Don8217;t leave it in the car with the window rolled up.8221;

In rare cases, some batteries can overheat on their own. Wozniak uses the phrase 8220;thermal runaway8221;, a term that can mean anything from toasting a user8217;s lap to catching fire. Manufacturers now include special circuits in laptop batteries to watch for this and, if detected, shut down the system. Wozniak says it is dangerous for home users to take apart their laptop batteries to replace the individual cells inside the plastic housing because the fail-safe circuitry may be damaged.

A second important step is keeping the contacts to the battery clean. An eraser is an ideal accessory for any charging station because it8217;s one of the simplest ways to remove the thin layer of oxide that can build up on the two metal tabs of the battery. Make sure to clean the contacts on the device as well and then blow away any eraser bits.

Opinions vary on the best way to avoid frequent recharging. The advice depends heavily on the type of battery. Wozniak, for instance, suggests disconnecting your battery if you use your laptop as a desktop replacement. The heat and the constant charging wear it down. He says some laptop manufacturers were beginning to explore circuitry that would help avoid this problem, but were confounded by the problem of anticipating just when the customer would unplug the laptop and expect it to be 100 per cent ready. The best solution, he says, is to leave the battery half-charged in a cool room and charge it completely just before using the laptop.

James DeJager, the technical director for Kodak batteries, sees nothing wrong with frequent recharging, at least for the lithium-ion batteries that are now standard in laptops and cellphones. 8220;For a lithium-ion, consumers should feel free to top them off as often as possible8230; If you8217;ve taken your cellphone with you and you8217;ve only used it a little bit, you8217;re extending your cycle life by topping it off and preventing a deep discharge.8221; He says he understands the argument for disconnecting the battery, but adds the circuitry can handle constant charging.

Much of the confusion comes from nickel-metal hydride cells, the previous generation of battery technology, which work better if they are often depleted completely before recharging. These batteries are now used mainly in digital cameras, flashlights and power tools. They can lose capacity if they are not discharged completely, often called the 8220;memory effect8221;.

Newer lithium-ion cells do not suffer from this malady, but users might want to deplete their batteries from time to time anyway. The circuitry that estimates the amount of power left inside a battery can become uncalibrated. Depleting the battery resets this meter.

Incidentally, Wozniak says better circuits are now appearing that measure the battery8217;s charge directly, avoiding cumulative accounting. 8220;By this time next year we won8217;t be manufacturing batteries with faulty fuel gauges,8221; he predicts.

The third important step is to match the battery to the job. While all batteries deliver power, some handle low, drawn-out demand better while others excel at heftier currents. Orlov, for instance, uses rechargeable cells in his robots but regular alkaline batteries for wall clocks and remote controls.

Why? Traditional rechargeable cells leak a relatively large amount of power, whether being used or not. A rechargeable battery in a remote control will probably lose more energy to leakage than it will use for channel surfing. Alkaline cells leak far less and last longer.

That is beginning to change as manufacturers create rechargeable batteries that leak less. DeJager is particularly proud of a new line of nickel-metal hydride batteries with a shelf life four times longer than its predecessor8217;s. Kodak calls them 8220;precharged8221; to emphasise that they can be used right out of the package. These batteries may hold their charge longer in storage, but they come with smaller capacity.

Isidor Buchmann, the founder of Cadex Electronics, which makes battery testing equipment, says the manufacturers and the consumers are in an eternal struggle. Just as the battery companies find a new set of chemicals that offer solid performance in an acceptable shape, consumers are demanding more performance from their electronics8212;performance that uses more power.

8220;In the 1990s, there was a battery problem,8221; he says, but now the lithium-ion cells have been good at delivering the power devices need to accomplish all that consumers expect.
Buchman holds no illusions: 8220;There will be a battery problem again with the new cellphones and all of the things people want to do.8221; 8212; NYT