Many mathematical models have been developed for Li-battery cells performances. However, a critical need still do exists for a rather simple battery performance evaluation method. In the present study, such a parameter, Integral average voltage (IAV), is being introduced. Its utility, convenience and applicability are validated via existing experimental data derived from Li-air batteries and lithiated Ni dope Mn spinel 5V cathode materials. IAV is simple to calculate using the cell charge/discharge profile; at the same time, it offers a perceptive analysis of cell features and associated processes.