January 1, 2009
Basics
To Save Battery Life, Turn Down the Heat
By PETER WAYNER
NIKOLAI ORLOV builds electronic gadgets for a living, so he’s pretty
demanding. When he comes home and wants to build robots with his
14-year-old daughter, Alexandra, he wants the batteries to be charged
and ready.
“They eat batteries really fast because they have three motors,” said
Mr. Orlov, a Silicon Valley-based hardware engineer.
One day Mr. Orlov noticed his charger wasn’t filling the cells to the
top. Because he is an engineer, he reached for his multimeter and
oscilloscope and checked the current. After a few days, he found a
malfunction in the circuit and fixed it by soldering in a few extra
components (capacitors, to be exact). Soon, the batteries were fully
charged.
While most people have neither his tools nor his skills, everyone can
relate to Mr. Orlov’s frustration when it comes to battery life. It
sometimes feels as if an advanced degree is necessary just to keep our
phones, P.D.A.’s and laptops running for more than a few minutes.
Fortunately, there are some simple principles that solve many of the
most common problems — and none of them requires a master’s or a Ph.D.
Battery experts say their No. 1 problem is heat. Too much warmth causes
the battery to drain faster. John Wozniak, a technologist at
Hewlett-Packard responsible for testing batteries, had some advice for
the owner of a battery-powered device: “You don’t want to leave it
sitting on the front seat of a car. It’s like the care and feeding of
the baby. Don’t leave it in the car with the window rolled up.”
In rare cases, some batteries can overheat on their own. Mr. Wozniak
uses the phrase “thermal runaway,” a term that can mean anything from
toasting a user’s lap to catching fire. Manufacturers now include
special circuits in laptop batteries to watch for this and, if detected,
shut down the system.
Mr. Wozniak said that it was dangerous for home users to take apart
their laptop batteries to replace the individual cells inside the
plastic housing (a cost-saving measure described by some
do-it-yourselfers on the Internet) because the fail-safe circuitry may
be damaged in the soldering and unsoldering process.
A second important step is keeping the contacts to the battery clean. An
eraser is an ideal accessory for any charging station because it’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. Mr. 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 said that some laptop manufacturers like H.P. were beginning to
explore adding 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 percent 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 many laptops and cellphones. “For a
lithium-ion, consumers should feel free to top them off as often as
possible,” he said. “If you’ve taken your cellphone with you and you’ve
only used it a little bit, you’re extending your cycle life by topping
it off and preventing a deep discharge.”
He says he understands the argument for disconnecting the battery but
says the circuitry can handle such constant charging. Furthermore, he
said in an e-mail message, it was “better to keep the contacts clean and
avoid the possible damage from repeated insertion/removal of battery.”
Much of the confusion about this point 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 “memory effect.”
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, Mr. Wozniak says that new and better circuits are now
appearing that measure the battery’s charge directly, avoiding
cumulative accounting. “By this time next year we won’t be manufacturing
batteries that have faulty fuel gauges on them,” he predicted.
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.
Mr. 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 new rechargeable
batteries that leak less. Mr. DeJager said he was particularly proud of
a new line of nickel-metal hydride batteries with a shelf life four
times longer than its predecessor’s. Kodak calls them “precharged” to
emphasize that they can be used right out of the package. Mr. De- Jager
jokes that some at Kodak wanted to call them “low self-discharge,” an
accurate term with an unfortunate abbreviation.
These batteries may hold their charge longer in storage, but they come
with smaller capacity. The precharged batteries from Kodak are rated to
hold 2,100 milliamp hours of power that last about 19 percent less time
before needing recharging than what Mr. DeJager calls the “original
recipe” with capacities of 2,500 or 2,600 milliamp hours. Trading
capacity for shelf life also affects the number of times a battery can
be used and recharged. Mr. DeJager estimates that the fatter
2,600-milliamp-hour batteries can be refilled about 500 times in ideal
circumstances. The 2,100-milliamp-hour cells may endure twice as many
recharging cycles.
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 electronics — performance that
uses more power.
“In the 1990s, there was a battery problem,” he said, but now the
lithium-ion cells have been good at delivering the power devices need to
accomplish all that consumers expect. With the air of a banker
discussing the business cycle, Mr. Buchman holds no illusions: “There
will be a battery problem again,” he said, “with the cellphones and all
of the things people want to do.”
Copyright 2009 The New York Times Company
Similar Threads
Linear Mode
