A charger and a charger controlling method for a battery rod having a small battery capacity are provided, which are used to charge a battery rod comprising a charging management circuit, and the battery capacity C of the battery rod is less than 100 mAh. The method comprises: defining a preset constant charging current I based on the battery capacity C of the battery rod in order to charge the battery rod with a current of KC, wherein, the value of K is less than 1, and the value of I and the value of C conform to the following relationship: I=K*C; detecting a real-time charging current Itemp of the battery rod in real time; comparing Itemp with I, and adjusting the output charging voltage according to the comparison result to charge the battery rod with a current of KC.