Nippon Telegraph and Telephone Corp. (NTT) has developed a prototype battery charger that is equipped with a solar panel to generate power, it said Friday.

The new external charger can provide voltage output between 3.8 volts and 8.5 volts, allowing it to be used for any electronic device that uses electric power of up to 5 watts. That makes it suitable for the majority of mobile devices such as cell phones, PDAs (personal digital assistants) and compact digital still cameras, Yuji Ikeda, a spokesman at NTT Information Sharing Laboratory Group, said in a response via e-mail to questions.

The charger consists of a solar panel, a rechargeable battery and an electric power converter, plus a cable to connect it to a mobile device, Ikeda said.

When the panel is exposed to direct sunlight for two hours, it generates about 2.4 watts/hour (Wh) of power that can fully charge its battery. That power is stored until the user needs it, and can then charge a cell phone or other device. It will allow a phone to be used for two hours of voice calls, Ikeda said.

The charger can also be used with an AC adaptor and plugged into a normal power outlet.

It measures 19 centimetres by 9 centimetres by 2.1 centimetres and NTT hopes to reduce this size to something similar to a cigarette box by commercialization. However, NTT’s research and development centre does not have a planned commercialization date yet, Ikeda said.