The desired performance characteristics and physical requirements of spacecraft batteries for planetary exploration are reviewed, particularly with respect to surface landers and revers intended for near-future Mars missions. The use of lithium ion batteries is justified in terms of significant savings on mass and volume, and more importantly of superior low temperature performance deemed essential in the Mars lander and rover missions. Use of these batteries in planetary orbiters may require further improvements in their cycle life, especially at low depths of discharge. Various strategies currently being adopted to prolong the cycle life for orbiter applications, as well as, for extending their operating range down to temperatures as low as -30 degrees C for more imminent Mars lander and rover missions are briefly discussed. (C) 2000 Elsevier Science Ltd. All rights reserved.