A device for controlling electric power, comprising: control means (15, 100) configured to specify a voltage detection period; and detecting means for detecting voltage between terminals of a battery and configured to detect an open-circuit voltage, during the voltage detection period based on the voltage of the battery; characterized in that it further comprises: switching means connected between the battery for supplying a load with electric power and the load, the switching means configured to switch between turning electricity on and off; and predicting means (101, 102, 103) configured to predict load power characteristics indicating characteristics of power consumed by the load over time, and to predict, based on the predicted load power characteristics, charge/discharge power characteristics indicating characteristics of charge/discharge power of the battery over time; further characterized in that: the control means (15, 100) is further configured to control the switching means and is configured to specify from the charge/discharge power characteristic that is predicted by the predicting means (101, 102, 103) a period as the voltage detection period, during which the charge/discharge power of the battery is equal to or less than a prescribed power over a prescribed period, and the detecting means is further configured to detect the open-circuit voltage, during the voltage detection period, after the switching means is turned off. control means (15, 100) configured to specify a voltage detection period; and detecting means for detecting voltage between terminals of a battery and configured to detect an open-circuit voltage, during the voltage detection period based on the voltage of the battery; characterized in that it further comprises: switching means connected between the battery for supplying a load with electric power and the load, the switching means configured to switch between turning electricity on and off; and predicting means (101, 102, 103) configured to predict load power characteristics indicating characteristics of power consumed by the load over time, and to predict, based on the predicted load power characteristics, charge/discharge power characteristics indicating characteristics of charge/discharge power of the battery over time; further characterized in that: the control means (15, 100) is further configured to control the switching means and is configured to specify from the charge/discharge power characteristic that is predicted by the predicting means (101, 102, 103) a period as the voltage detection period, during which the charge/discharge power of the battery is equal to or less than a prescribed power over a prescribed period, and the detecting means is further configured to detect the open-circuit voltage, during the voltage detection period, after the switching means is turned off. switching means connected between the battery for supplying a load with electric power and the load, the switching means configured to switch between turning electricity on and off; and predicting means (101, 102, 103) configured to predict load power characteristics indicating characteristics of power consumed by the load over time, and to predict, based on the predicted load power characteristics, charge/discharge power characteristics indicating characteristics of charge/discharge power of the battery over time; further characterized in that: the control means (15, 100) is further configured to control the switching means and is configured to specify from the charge/discharge power characteristic that is predicted by the predicting means (101, 102, 103) a period as the voltage detection period, during which the charge/discharge power of the battery is equal to or less than a prescribed power over a prescribed period, and the detecting means is further configured to detect the open-circuit voltage, during the voltage detection period, after the switching means is turned off. the control means (15, 100) is further configured to control the switching means and is configured to specify from the charge/discharge power characteristic that is predicted by the predicting means (101, 102, 103) a period as the voltage detection period, during which the charge/discharge power of the battery is equal to or less than a prescribed power over a prescribed period, and the detecting means is further configured to detect the open-circuit voltage, during the voltage detection period, after the switching means is turned off.