Japanese company Rohm is showing tiny hydrogen fuel cells meant for charging portable gadgets at the Ceatec exhibition just outside Tokyo.
The cells are 32mm by 65mm, slightly larger than a nine-volt battery, and easily fit in the palm of the hand. They are snapped into a case about the size of a smartphone for use, which outputs electricity through a USB connection.
A sample on the show floor produced some heat, but not enough to be uncomfortable to the touch.
Rohm, which aims to bring the cells to market from April of next year, says each one produces 5 watt hours of power, enough to charge a smartphone in about two hours. The company is working with the smaller firm Aquafairy on the technology.
"The cartridges will cost about the same as equivalent batteries on sale today," said Kazuhiro Tatsumi, a research manager at Aquafairy.
He declined to give a price for the reusable cases, but said they will likely be under 10,000 yen (£80).
The companies say the main advantages of the cells are that they are very stable and can be stored for 20 years without losing effectiveness, their relatively high power output, and the benign casing left over when they are depleted, which can be thrown away with ordinary trash.
Disadvantages include the need for the separate casing to use them and the fact that they can't be recharged.
The cartridges contain small sheets of calcium hydride and water, which are mixed to produce hydrogen when they are snapped into the larger casing. As in other fuel cells, the hydrogen is then converted to electricity. Calcium hydride has more commonly been used to quickly inflate weather balloons and life vests.
As the cartridges contain a potentially dangerous substance, they won't be allowed on airplanes and are not well suited for extreme environments. The company has rated them as safe from between 5 and 40 degrees Celsius.
The companies are also planning to produce larger fuel cells using the technology, and are showing one about the size of a desktop computer at Ceatec.
Ceatec, Japan's largest electronics show, runs this week in Makuhari, just outside of Tokyo.