By ANNE EISENBERG

AS circuitry and components become smaller and smaller, the bulkiest part of a portable electronic device these days is often the battery, which comes packed in a stiff and heavy metal case.

Now a small Israeli company has devised caseless batteries that are printed directly onto paper, plastic or other surfaces.

The thin, flexible batteries may soon be plastered on cardboard or plastic surfaces, producing novelty packaging items like cereal boxes that twinkle with light-emitting diodes or containers that advertise their wares by playing brief jingles.

Smart labels and cards might one day use these batteries, too. Plastic payment cards, for instance, might have on-board batteries to power tiny embedded chips linked to liquid-crystal displays that show an account balance, frequent-flier miles or other data. Gilles Lisimaque, a founder of Gemplus, a smart-card manufacturer, said, "You could add an L.C.D. display powered by the battery, and the card can tell you how much money is left without going to a terminal."

And smart labels with microprocessors and sensors, each powered by a paper-thin battery, might keep track of the goods beneath their labels. For instance, labels on blood bags might monitor the temperature of the blood while it was in transit.

The battery makes electricity in the same way as conventional batteries, with two electrodes -- a cathode and an anode -- separated by electrolytes, ions that conduct electricity. "This is a conventional zinc-manganese dioxide battery, with the usual anode and cathode," said Baruch Levanon, chief executive of Power Paper, the private company that developed the battery.

"The difference is in the formula for the electrolytes," Mr. Levanon said. "We call it our Coca-Cola formula because the chemistry of the ink we used to print the electrolytes is a secret."

Usually the moist paste of electrolytes must be encased in metal. Here, though, the electrolytes, like the anode, cathode and conductors, are printed in layers directly on the paper or plastic surface.

The cell, which is about as thick as the paper in a milk carton, produces 1.5 volts and has a shelf life of two and a half years, Mr. Levanon said. It is not rechargeable and is designed to be used with disposable products with modest current requirements for powering things like an L.C.D. or a small microprocessor. Because the battery is so flat, its capacity is proportional not to its volume, as would be the case, for instance, in D-size batteries, but to its area. To produce as much energy as an AA alkaline battery, for instance, the paper battery would need to cover about a square foot.

"The more area, the more energy," Mr. Levanon said, "so you adjust the battery to the needs of the product, not vice versa."

Several companies, including International Paper, based in Purchase, N.Y., have signed licensing agreements with Power Paper. Mr. Levanon said his company would also be producing paper novelty items at its own factory in Hong Kong.

One of the first microelectronic products to use Power Paper batteries may be on the market by the end of this year, said Dr. Thomas Seidowski, president of KSW Microtec, a company based in Dresden, Germany, that produces microassemblies, like the components of radio-frequency identification cards. KSW has developed a smart label to monitor the temperature of packages of blood while they are being shipped.

The label includes a chip, the Power Paper battery, a temperature sensor and a radio frequency antenna and a transponder. "We need the battery to start the operation, for sensing, and to store data," Dr. Seidowski said. The chip is programmed to check the temperature at intervals, and the information is communicated by the radio frequency interface. "We are using the transponder interface to talk with the chip, to load software to it and to read the history of transportation and storage," he said. "For this we must have a power supply integrated on the chip." Dr. Seidowski estimated that the labels would cost about $2 each when produced in quantity.

The Power Paper batteries are "a good technology for throwaway items, for instance, smart cards or labels," said Sol Jacobs, vice president and general manager of Tadiran Electronic Industries of Port Washington, N.Y. Tadiran makes the lithium batteries in the electronic badges used with the E-ZPass toll-collection system.

The paper battery, or ones similar to it, may one day be used in the nascent field sometimes called paper electronics, helping to produce electronic books or newspapers on thin, flexible pages that can be thumbed through nearly as easily as printed pages.

"We are interested in thin, flexible batteries with paperlike appearance and behavior," said Nicholas K. Sheridon, a physicist who is the inventor of an electronic paper technology named Gyricon. Mr. Sheridon is the research director at Gyricon Media, in Palo Alto, Calif., a Xerox subsidiary.

The electronic ink in Mr. Sheridon's system uses small balls that are black on one hemisphere and white on the other. They rotate in response to a voltage to form an image. Mr. Sheridon said one of Gyricon's interests was in developing electronic signs for retail use. The signs could be kept up to date through radio-frequency links to the store's computer system.

"E-books and e-newspapers are farther in the future," he said.

Mr. Levanon, of Power Paper, said the company would have a rechargeable version of the battery within a year or so. "Once you have the energy and the display in a flexible device," he said, "you can have an organizer the thickness of a credit card."

GRAPHIC: Photos: POWER TO GO -- Printed batteries on paper or plastic could lead to payment cards that display account balances with L.E.D. displays.