According to one embodiment, a battery control device includes a charge and discharge circuit and a processor. The processor determines, based on an information regarding a secondary battery electrically connected to the charge and discharge circuit, whether or not a diagnosis implementation condition is satisfied; controls the charge and discharge circuit to charge the secondary battery only after discharging or charging up to a charging-start SOC if the diagnosis implementation condition is satisfied; acquires measurement data of a voltage and a current of the secondary battery while charging; estimates an internal state parameter of the secondary battery based on the measurement data; and diagnoses a deterioration state of the secondary battery based on the internal state parameter of the secondary battery.