Tool batteries

A battery housing (32, 34) of a tool battery (30) has a hook accommodation chamber and a battery cell accommodation chamber defined therein. A hook (50) is accommodated within the hook accommodation chamber and is operable to lock and unlock the tool battery (30) against a tool body (20) of a power tool. Battery cells (S) are disposed within the battery cell accommodation chamber. The hook accommodation chamber and the battery cell accommodation chamber are partitioned from each other.