A novel method was proposed to judge degradation/health of lithium-ion batteries using the capacitance that was estimated from the real-time voltage and current characteristics of the batteries. It is thought that the capacitance of lithium ion batteries decreases with degradation because of undesirable components formed on the electrodes that are the main cause of the degradation. As the lithium ion batteries are active, the capacitance was evaluated from the differential equation, ΔQ/Δv = I/(Δv/Δt) = i/(dv/dt), using the voltage and the current characteristics during the charging or the discharging. The capacitances of the commercial LIBs with different SOHs; 100, 92 and 88% were estimated during the charging and the discharging using the equation. The average capacitance in the specific voltage region of the batteries was directly proportional to the state of health. Therefore, the proposed measurement is thought to be a useful method for judging degradation of lithium-ion batteries.