Rechargeable battery pack for a power tool

摘要

A battery pack (20) for a power tool of self-contained over-charge protection is proposed. The battery pack includes a battery stack composed of a plurality of series connected secondary cells (24), and a charge terminal (33) connected through a charge current path to the battery stack for flowing a charge current from a charger. The battery pack includes an interrupter (93) inserted in the charge current path, and an over-charge detector (90) which detects a cell voltage across each of the secondary cells and actuates the interrupter to open the charge current path when any one of the cell voltages becomes higher than a predetermined threshold (V TH3 ). Thus, even if the charger fails to limit the charge current, the battery pack can itself protect the secondary cells from being over-charged.