Mg Box: Magnesium phone battery runs on water

A Japanese company said its water-powered emergency battery generates enough juice to charge a smartphone up to 30 times.

Furukawa Battery announced the Mg Box, pronounced Mug Box, generates electricity for about five days once about 2 quarts of water are poured in and react with the magnesium inside.

The company said the magnesium-air battery, designed as an emergency preparedness item, generates about 300Wh, enough electricity for up to five days.

The box will go on sale in mid-December for about $93, the company said.