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CELLPHONES will begin to run low on power over the next few years as advances in battery technology fail to keep up with the demands of the numerous energy-draining features being planned by mobile phone makers.

That was the warning from Yrj枚 Neuvo, chief technology officer of Finnish cellphone giant Nokia. Speaking at the International Solid State Circuits Conference in San Francisco last week, Neuvo predicted that piling high-resolution still cameras and video displays and high-speed internet access into ever-shrinking mobile phones is likely to become too much for small batteries to cope with. 鈥淭here is no silver bullet that will help us cut down on power consumption,鈥� he says.

Thanks to lithium-ion technology, batteries have tripled their energy output per unit volume in the past 10 years, but this has not been enough to keep up with advances in chip design. Microchips have been getting denser according to 鈥淢oore鈥檚 law鈥�, which holds that the number of transistors on a chip roughly doubles every two years.

Neuvo predicts that battery capacity will have to rise by 10 per cent a year to support the ever-increasing number of features available on mobile phones, often called 鈥渇eature creep鈥� (see 鈥淭hat鈥檚 the way the power goes鈥�). But battery experts say achieving this will be almost impossible. They say batteries will have to be charged more frequently, perhaps many times a day, and that they will wear out more quickly as they can only be charged a few hundred times before they degrade. And applications will simply fail if batteries cannot produce the surge of power needed to run them at the same time as others.

It is already happening. In Japan, there are phones that are incapable of delivering advertised features because their batteries are not powerful enough, says Isidor Buchmann, founder of Cadex Electronics in Vancouver, Canada, which makes battery chargers. Others say the fact that Apple鈥檚 popular music player, the iPod, often needs replacement rechargeable batteries after just 18 months, is evidence that batteries are already failing to keep pace.

鈥淧eople want more and more power for their various applications and they want it all smaller. But at some point the battery becomes the driver of the technology,鈥� says Dennis Dees, a battery researcher at Argonne National Laboratory in Illinois.

A battery comprises a negative and a positive terminal, separated by an electrolyte medium. When a wire connects the terminals, a chemical reaction allows electrical charge to flow from one terminal to the other.

Cellphones use lithium-ion batteries 鈥� the highest-power rechargeable batteries available. The negative terminal is composed of lithium ions surrounded by matrices of carbon atoms. The positive terminal is made of cobalt oxide. When a wire connects the terminals, the lithium ions move to the positive terminal to form lithium cobalt oxide, creating a net flow of charge.

To get more power out of a battery, more charge has to flow. To do that, battery makers must either get more lithium ions migrating or make those that do move faster.

But more ions means a bigger battery, and mobile phones are shrinking. Battery scientists are experimenting with alternatives to the carbon matrix and cobalt oxide to speed up ion migration, but no one is expecting a dramatic increase even if they are successful. Khalil Amine, also a battery researcher at Argonne, says, 鈥淭hey have reached the limit for any improvement they are going to get. We now have a stagnation situation with lithium-ion batteries.鈥�