An embodiment of the invention provides a method and a device for acquiring capacity difference between batteries. On one hand, a battery pack is charged in a designated charging mode, the time integration result of the current of each battery in the battery pack between a first moment and a second moment is acquired in the charging process, the first moment is the moment that the voltage of each battery reaches first voltage, the second moment is the moment that the voltage of the battery with the highest voltage in the battery pack reaches second voltage, and then the capacity difference every two batteries in the battery pack is acquired according to the integration result of each battery in the battery pack. Therefore, the problem of incapability of acquiring the capacity difference every two batteries in the battery pack when the current flows through the battery pack in the prior art can be solved.