A battery testing device which can charge a chargeable secondary battery by using charging means for charging said secondary battery, the device comprising: input control means for controlling input power which said charging means inputs to said secondary battery; and output control means for controlling output power which is output from said secondary battery, and discharging said secondary battery, wherein the output control means is further configured to, when said secondary battery reaches a fully charged state, start discharging said secondary battery while said input control means stops charging said secondary battery using said charging means, and wherein the input control means is further configured to, when said secondary battery reaches a predetermined charged state, start charging said secondary battery using said charging means while said output control means stops discharging said secondary battery, wherein the battery testing device further comprises temperature adjustment means for adjusting temperature of said secondary battery, wherein said input control means is further configured to control input power which is input to said secondary battery at a temperature adjusted by said temperature adjustment means, using said charging means, and said output control means is further configured to discharge said secondary battery by controlling output power which is output from said secondary battery at a temperature adjusted by said temperature adjustment means;. wherein said temperature adjustment means is further configured to make an adjustment to hold the temperature of said secondary battery at 50°C, wherein said input control means is further configured to control input power, which is input in use of said charging means, to said secondary battery at 50°C adjusted by said temperature adjustment means, and said output control means is further configured to discharge said secondary battery by controlling output power which is output from said secondary battery at 50°C adjusted by said temperature adjustment means, characterized in that said temperature adjustment means is further configured to make an adjustment to hold the temperature of said secondary battery at 150°C for three hours when the battery capacity of said secondary battery reaches a predetermined capacity by repeat of discharge of said secondary battery by said output control means and charge of said secondary battery using said charging means by said input control means, and wherein said temperature adjustment means is further configured to judge whether the temperature of said secondary battery rises to 160°C or more while performing adjustment to hold the temperature of said secondary battery at 150°C for three hours, and to display a result of the judgment on an external device. input control means for controlling input power which said charging means inputs to said secondary battery; and output control means for controlling output power which is output from said secondary battery, and discharging said secondary battery, wherein the output control means is further configured to, when said secondary battery reaches a fully charged state, start discharging said secondary battery while said input control means stops charging said secondary battery using said charging means, and wherein the input control means is further configured to, when said secondary battery reaches a predetermined charged state, start charging said secondary battery using said charging means while said output control means stops discharging said secondary battery, wherein the battery testing device further comprises temperature adjustment means for adjusting temperature of said secondary battery, wherein said input control means is further configured to control input power which is input to said secondary battery at a temperature adjusted by said temperature adjustment means, using said charging means, and said output control means is further configured to discharge said secondary battery by controlling output power which is output from said secondary battery at a temperature adjusted by said temperature adjustment means;. wherein said temperature adjustment means is further configured to make an adjustment to hold the temperature of said secondary battery at 50°C, wherein said input control means is further configured to control input power, which is input in use of said charging means, to said secondary battery at 50°C adjusted by said temperature adjustment means, and said output control means is further configured to discharge said secondary battery by controlling output power which is output from said secondary battery at 50°C adjusted by said temperature adjustment means, characterized in that said temperature adjustment means is further configured to make an adjustment to hold the temperature of said secondary battery at 150°C for three hours when the battery capacity of said secondary battery reaches a predetermined capacity by repeat of discharge of said secondary battery by said output control means and charge of said secondary battery using said charging means by said input control means, and wherein said temperature adjustment means is further configured to judge whether the temperature of said secondary battery rises to 160°C or more while performing adjustment to hold the temperature of said secondary battery at 150°C for three hours, and to display a result of the judgment on an external device.