A new approach on vehicular fuel cell technology uses an on-board regenerative fuel cell (RFC) stack as a battery charger. The RFC's electrolyser capability uses grid electricity to produce hydrogen and oxygen during an overnight charging process. By using the RFC to recharge the vehicle's battery pack during the day, the size of the battery pack can be reduced by > 50%. A sensitivity analysis evaluating vehicle specification and component perfon-nances suggests that small RFC stacks (e.g. 1 kW) would be commercially viable in plug-in vehicles at prices as high as $1800/kW for the RFC stack. The combination of a RFC stack and a battery pack would cost less than the either an appropriately sized battery pack or fuel cell stack alone. Vehicles using so-called tribrid power systems based on the combination of RFCs, battery packs, and internal combustion engines (ICE) could be viable decades before vehicles powered solely by fuel cells that rely on a hydrogen refueling infrastructure. (C) 2004 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.