Power tool battery pack

A power tool battery pack (10) comprises a lower side case (21), an upper side case (23) fixed to the lower side case, at least one battery cell (33) housed in the lower side case, a circuit board (42) electrically connected to the battery cell and first and second terminals (51, 511-516) disposed on and connected to the circuit board. To isolate the first and second terminals and prevent undesired electrical connection due to, e.g., a water droplet contacting both of them, a slit (61) extends through the circuit board (42) between the first terminal and the second terminal.