Under normal circumstances, in the charge and discharge process, due to the larger current, and the battery has a certain internal resistance, then the battery heat and the temperature increased. However, when the battery charging current is too large, the gap between the batteries is too small and heat dissipation is poor, the temperature rise will increase the float charge current, which will cause the battery to further generate temperature rise, and cause thermal runaway until the battery is damaged. The accuracy of charging equipment is not enough. Although the charging equipment has been filtered, it still has ripple voltage which occur temperature rises and battery life, and battery damaged.