To facilitate confirmation of the history of a battery unit even if the battery unit is used by unmanned carriers one after another, by causing each battery unit itself to have a battery managing means which manages the history of the unit.

About one to six battery units 4 each of which has a battery managing means 6 are mounted on each unmanned carrier. After use, the units are unmounted from the unmanned carrier, charged uniformly, and used by other unmanned carriers. Here, the battery units 4 are charged by a charger 14, and along with it performance of uniform charging or rapid charging, and a present date of charging at the time of uniform charging are reported to their respective battery managing means 6. In the battery managing means 6, battery management numbers and dates of use are written in a memory 24, and one is added to the number of times of uniform charging at each uniform charging, and the date of uniform charging is renewed to a final date of uniform charging. These pieces of information represent periods of use and the numbers of times of charging of the battery units 4, and make it possible to predict their lives.