The temperature of battery modules in electric vehicles (EVs) must be controlled adequately to remain within a specified range for optimum performance. In this paper, thermal management of battery modules with phase change materials (PCMs) is investigated experimentally. An electric heater is used to simulate the heat source of a battery cell. Two different PCM designs are investigated: one with a PCM cylinder surrounding the heater, and the other with PCM jackets wrapping the heater. Both configurations exhibit good effectiveness in maintaining the heater within a desired temperature range. This paper also examines the effectiveness of PCM thermal management under variable heating rates and variable ambient temperatures, as well as the effects of buoyancy during PCM melting. (C) 2010 Elsevier Ltd. All rights reserved.