Electrochemical performance of the natural graphite (Mag-10)/Li half-cell, LiNi0.8Co0.15Al0.05O2 /Li half-cell, and LiNi0.8Co0.15Al0.05O2 / Mag-10 full-cell are discussed in terms of reversible and irreversible capacity. Heat rate profiles of these cells cycled at various current levels are studied in terms of reversible and irreversible heat generation. The experimental data show an excellent agreement with the calculated results at low and moderate current levels (less than or equal to C/5). The quantitative heat contributions of the cathode and anode to the overall cell heat generation are also determined. (C) 2004 The Electrochemical Society.