In this paper, the Ni-Cd battery principle and exothermal processes are first recalled. It is pointed out that heat generation can be decomposed into irreversible losses (entropic effect), battery electric resistance and polarization effect. It is shown how these effects can be analyzed from overall battery heat balance. The calorimetric test bench is described. Battery cycles are composed of charge, overcharge, rest and discharge. Typically, the total heat losses range around 25% with an increase up to 33% at 200 A. Only during overcharge, gas losses are shown to be a high contribution. The paper shows that the calorimetric study permits not only further insight into local temperatures and heat losses, but also to deduce such parameters as entropy generation and, above all, total resistance (Joule effect and polarization). In this case, resistance was estimated to increase from 2 to 6 mOmega with depth of discharge from 0 to 100%. (C) 2003 Elsevier Science B.V. All rights reserved.