Rechargeable battery protecting apparatus and power storage system

A rechargeable battery protecting apparatus comprising:

• a deteriorated capacity calculator to calculate, from a voltage and a current of a cell contained in a rechargeable battery, a deteriorated capacity that is a capacity by which a capacity of the cell that is in an initial state is reduced;
• a gas amount calculator to calculate, from the deteriorated capacity calculated by the deteriorated capacity calculator, an amount of gas contained in a container for the cell;
• a pressure calculator to calculate pressure inside of the container from the amount of the gas calculated by the gas amount calculator, a void volume of the container for the cell, and a temperature of the cell;
• and
• a pressure monitor to determine whether to output a control signal for protecting the rechargeable battery based on whether pressure inside of a container that is calculated by the pressure calculator is equal to or greater than a threshold pressure with respect to at least one cell.