Battery pack and battery charger

A battery pack (10) includes: a connecting portion (14A, 14B, 16A, 16B) connected to a battery charger; a battery (20) chargeable by the battery charger (40) connected to the connecting portion (14A, 14B, 16A, 16B); an environment temperature detecting element (32) detecting an environment temperature around the battery; and a control circuit (34). The control circuit (34) periodically detects the environment temperature via the environment temperature detecting element (32) and controls the battery charger (40) to suspend starting of charging the battery (20) or to temporarily discontinue charging the battery (20) when a variation of the environment temperature detected exceeds a predetermined range, when the battery charger (40) is connected to the connecting portion (14A, 14B, 16A, 16B).