Patent ID: 8330426

Claim:
A charging system for electric power tool, comprising a battery pack and a battery charger, wherein the battery pack is used for driving an electric power tool and the battery pack has a rechargeable battery (B 1 , B 2 , . . . Bn) serving as a power source for driving the electric power tool, and a battery-side microcomputer which is a microcomputer monitoring a state of the rechargeable battery (B 1 , B 2 , . . . Bn); wherein the battery charger is detachably mounted with the battery pack and the battery charger has a charging unit, which supplies a charging power to the battery pack and charges the rechargeable battery (B 1 , B 2 , . . . Bn), and a charger-side microcomputer which is a microcomputer controlling an operation of the charging unit, wherein at least while the rechargeable battery (B 1 , B 2 , . . . Bn) is charged by the charging unit, the battery-side microcomputer and the charger-side microcomputer mutually perform data communication and execute mutual operation confirmation for confirming an operational state of a microcomputer of a communication counterpart based on a result of the data communication, and when one of the battery-side microcomputer and the charger-side microcomputer detects an abnormality of the operational state of the microcomputer of the communication counterpart as a result of the mutual operation confirmation, a microcomputer which has detected the abnormality executes a predetermined charge stop processing for stopping charging of the rechargeable battery (B 1 , B 2 , . . . Bn).