A battery lock (10) includes a block (20), a locking mechanism (40) and a key assembly (70). Rotating the proper key will rotate the key mechanism (40) and a sleeve (50) disposed around a shaft (41), permitting the block (20) to pass by a pair of protuberances (150,151) within a cavity (144) to remove the lock (10) from a receptacle (141) or to lock the locking mechanism (40) behind the protuberances (150,151). In this manner, one can insert the battery lock (10) into the battery's (100) receptacle (141), secure the lock (10) in place and remove it.