An eco-friendly battery that can be munched by microbes has been developed by Nippon Telegraph and Telephone Corp. (NTT).

The idea is they will charge sensors that can be placed around volcanoes to note temperatures and vibrations, as well as in rivers to obtain data on water movement. Then when they die, the microbes have a feast.

It's branded as "the battery that will return to the earth" and is part of what is being called IoT ("Internet of things") technology in which a wide variety of objects are embedded with sensors.

The new technique has been developed to prepare for when Internet-equipped sensors cannot be recovered.

The triangular battery measures 2 centimeters along a side and boasts 1.1 volts, which would be enough for an LED lamp for 24 hours.

Eco-friendly sensors and communication chips to go with the battery are also being developed.

In the experiment, the newfangled batteries and regular ones were powdered and 1 gram of each was mixed into soil for two pots.

Seeds of Japanese mustard spinach were then sowed in the pot, and it was found that the eco-friendly batteries did not affect the growth whereas the vegetable did not grow in the pot with the regular battery mix.

A battery has an electrolysis solution between two electrical poles. In conventional batteries, electrical poles contain harmful rare metals, including lithium, and fluorine.

And the electrolysis solution is made of potassium hydroxide, a strong alkaline material that is not plant friendly.

NTT used biological materials that were carbonized for the poles and almost-electrically neutral liquid for the electrolysis solution.