Heat generation plays an important role for energy storage systems like batteries in electric and hybrid vehicles. In order to investigate the thermal and electrical behaviour the batteries were exposed to cycling programs including various methods of battery cooling by flowing air. Two different experimental methods were presented to study the establishing of the heat balance. The second part of the paper describes the simulation of the temperature distribution by using finite element methods (FEM). The electric and thermal battery model was compared with results obtained from temperature measurements at four selected points during battery cycling.