From thermal engine equipped vehicles to completely electric ones, evolution of light weight vehicles in the future will take several steps in so far as there is no adequate battery or fuel cell presently available to power these vehicles for “on the road” driving. On the other hand, for city driving, vehicles can be improved a lot in terms of fuel efficiency as well as air pollution, if partly or totally electric propulsion can be developed, manufactured and marketed for appropriate applications. The 36–42V battery is part of this orientation towards improving the efficiency of thermal vehicles in city driving, while keeping adequate autonomy on the roads. Actually, in city traffic, thermal engines are idle most of the time and stop periods represent a large part of the time spent “driving”, using up fuel and polluting air for no use at all. The idea of stopping the engine during these periods, if appropriately managed, might potentially lead to a large improvement in fuel economy as well as air pollution reduction. The association of a higher voltage battery to an alternator–starter device in thermal vehicles, seems to be an interesting way towards that end. In this paper, we are presenting our results of a study we have just completed in relationship with RENAULT & VALEO, supported by the French Ministry of Industry, concerning a comparative evaluation of different automobile energy storage systems, and the definition of specifications as the final step of this study. The main conclusion is that lead-acid will still remain dominant in this role, since its operational cost versus efficiency is by far the lowest of every battery presently considered, more particularly in the less expensive car segments.