I know some thought has been put into making a fuel cell hybrid vehicle. The fuel cell would be the primary power and the battery system would be the backup. The batteries charge just like hybrids do today. This doesn't answer your question of what to do if you run out of power but if someone manages to run out of hydrogen and then also run down the battery backup before refueling, then they probably deserve to be stranded.
NGCs 2005, ICs 103, Other 70, Palomar GCs 6, Abell PNs 12, Herschel 400: 316.
Celestron CPC 1100, Lunt 60mm Ha Solar Scope