On the occasion of the "Challenge Bibendum" 2004 in Shanghai, the hybrid fuel cell-supercapacitor vehicle HY-LIGHT, a joint project of Conception et Developpement Michelin and the Paul Scherrer lnstitut, was presented to the public. The drive train of this vehicle comprises a 30 kW polymer electrolyte fuel cell (PEFC) and a 250 V supercapacitor (SC) module for energy recuperation and boost power during short acceleration and start-up processes. The supercapacitor module was deliberately constructed without continuous voltage balancing units. The performance of the supercapacitor module was monitored over the 2 years of operation particularly with respect to voltage balancing of the large number of SC cells connected in series. During the investigated period of 19 months and about 7000 km driving, the voltage imbalance within the supercapacitor module proved negligible. The maximum deviation between best and worst SC was always below 120mV and the capacitor with the highest voltage never exceeded the nominal voltage by more than 40 mV. (C) 2007 Elsevier B.V.. All rights reserved.