Engineers at Japan's NEC have developed a battery less than a millimetre thick. The device can be charged to about 80 percent of its capacity in about 30 seconds

The battery has been designed for use in applications such as active RFID cards and could provide enough power to keep such cards running for several weeks before requiring a recharge, said Yoshimi Kubo, chief manager of fuel cell and battery research at NEC's fundamental and environmental research laboratories.

The device is an "organic radical battery," a technology developed by NEC that uses materials that are more environmentally-friendly than the chemicals found in common rechargeable batteries, the company said. NEC began researching the technology in 2000 and its work has been partly funded by Japan's New Energy and Industrial Technology Development Organization (NEDO).

Such thin batteries are important for active-type RFID cards. Most current RFID cards or tags are passive devices which aren't capable of transmitting data on their own and work when brought into proximity with a radio field from a tag reader. This typically means they work over a range of several centimetres. Active tags are more like miniature radios and can transmit over longer distances, which means they can be read without having to bring them so close to the tag reader.

NEC said it has no current plans for commercial production of the device or an estimate of how much it will cost at such a time as production begins.

It's not the first organic radical battery application developed by NEC. A larger version of the battery was shown earlier this year and proposed as a possible future emergency power source for personal computers. Because the battery is capable of delivering a large amount of power in a short period NEC demonstrated it being used to power a PC for about 15 seconds, which is enough time for the PC to back-up important data and shut-down properly.

That application used four batteries each of which measure 55 millimetres by 43 mm and are 4mm thick, which is about the same size a stack of 3 credit cards.