The battery battle between lithium-ion and zinc air begins

My previous column [GCN, Aug. 26, Page 55] looked at lithium-ion batteries,
the most popular batteries in the notebook market. A new lithium-based technology called
lithium polymer promises twice as much power per pound, but with half the expected
lifetime.


LiP batteries will last only about 10 percent as long as nicads before you must replace
them. At the moment, that doesn't seem appropriate for most portable computing.


Zinc-air batteries are another story. You can buy replacement zinc-air button batteries
now for devices such as pagers. The big advantage of zinc-air is that it will keep your
power-hungry Pentium portable lit up for the duration of a coast-to-coast flight and keep
on going all the way to Europe, even if you're not riding the Concord e.


The only zinc-air battery pack that's commercially available right now is the $370
PowerSlice from AER Energy Resources Inc. of Smyrna, Calif. This is a 3-pound, external,
adjustable 12- to 17-volt power supply.


Before you dismiss such a colossal size out of hand, remember my argument in the
previous column: The crucial weight isn't just the notebook but the total carry
weight--and bulk.


The PowerSlice could substitute for a spare battery plus battery charger and power
cord, so its weight is reasonable for 12 or more hours of operating time.


AER engineers have been working to improve zinc-air performance with a second air
electrode and greater air flow. These changes have increased capacity by about 80 percent
while cutting the recharge time in half and decreasing weight for a given capacity,
according to the company.


Current zinc-air batteries have excellent power-to-weight ratios. The PowerSlice looks
so big because it's built with massively higher capacity than the usual internal notebook
battery. In terms of watt-hour capacity, the latest zinc-air batteries weigh about half as
much as equivalent lithium ion and one-third as much as nickel-metal hydride. They have
about the same bulk as equal-power lithium-ion batteries.


Because zinc-air depends on atmospheric oxygen, it's relatively nonpolluting and, until
the sealing cover is broken, enjoys an incredibly long shelf-life with a discharge rate of
only about 2 percent a year.


We've all heard about the power-management technology being built into notebook
software and the microprocessors that can slow down in clock speed to conserve power
depending on the programs being run. But many still don't realize how smart battery packs
are getting.


They're becoming so common that Intel Corp. has published a smart-battery specification
for designers who want batteries to communicate with the notebook hardware.


Short-circuit protection was the first such smart capability built into battery packs.
Today's versions go much farther with charge-rate control and charge-capacity monitoring.


Battery monitoring is an important safety consideration --there have been a few
fires--but it's also important to designers of chemistry-independent computers.


Soon users will be able to select the optimum battery type for their applications.
Having the battery monitor and control its own charging means that chargers and power
supplies can be lighter and simpler, and nothing will have to be upgraded to accommodate a
new battery type.


With advances in zinc-air power density, and the ability of notebooks to ask internal
smart battery packs whether their chemistry depends on lithium, zinc or nickel, you can
expect that users will soon mix and match batteries to fit their needs.


When that happens, expect zinc-air batteries to become the top choice for people who
need to work a full day on a single charge. Although present technology limits this much
running time to the large'20external zinc-air battery packs, we soon should be getting
six to eight hours out of a small internal zinc-air battery.


Unless a drastic advance occurs elsewhere, it looks like the battery battle between
zinc-air and lithium is about to begin.


John McCormick, a free-lance writer and computer consultant, has been working with
computers since the early 1960s. He welcomes mail from readers. Write to him care of
Government Computer News, 8601 Georgia Ave., Suite 300, Silver Spring, Md. 20910.



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