A battery charging method and device thereof are disclosed. The method includes the following steps. First, a charging current is supplied into a plurality of cell blocks of a battery module for charging, and the terminal voltages of the cell blocks are detected, when one of said terminal voltages exceeds a first threshold, the charging is kept continuously over a first preset time period. If one of said terminal voltages of said cell blocks exceeds a second threshold, an over voltage protection is performed, else the charging current is reduced and the battery module is charged by the reduced charging current continuously over a second preset time period and if the cell blocks are determined that they are fully charged, the charging is stopped, otherwise, the battery module is charged continuously. Therefore, the battery charging method and device thereof in accordance with the present invention can prevent the battery module from being overcharged and prolong its life.