New battery runs on water

A new battery can be topped up simply by adding water, its developer claims.

The battery, sold in Japan under the name No Po Po, comes in standard AA and AA formats as well as larger sizes for use as auxiliary power supplies.

Literature from the Japanese developer, Aqua Power System, is short on details, as is the website. The AA battery is said to deliver 50 milliamps and the AAA 30 milliamps, both sufficient only for the most undemanding applications.

Staff on the company’s stand at the IFA consumer electronics show in Berlin said the batteries can last up to five hours between charges and release no dangerous gases. But they spoke little English and could not explain how the batteries work, other than that they were "voltaic".

The original Voltaic battery, invented by the Italian Alessandro Volta in 1800, used zinc and copper or silver electrodes dipped in salt water.

The new version uses an alloy of aluminium, magnesium and other metals and gained a UK patent in March this year, according to company literature.

This stresses the environmental friendliness of the new batteries compared with conventional dry-cell and lithium-ion products. But it seems that the electrodes degrade after a few uses, though the company says it has technology to retard this. A pack of four AAA batteries sells in Japan for around ₤3.50.