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