Water vapour issuing from the exhaust pipe is the sole sign of activity inside the cells as they quietly convert chemical energy into electricity.
That power then drives electric motors, often mounted on the wheel hub at the ends of the axles, to provide motion. Hydrogen propulsion has the edge over the all-electric solutions currently being tried out, and in the end it may outlive them all.
The technology has so far found its way into some expensive buses and forklift trucks, but no hydrogen-powered car has gone on sale despite the collective efforts of Honda, Mercedes-Benz, BMW and Opel to develop one.
They have been tinkering with the technology for years and numerous test-bed vehicles have proved their merit. Now car makers are jostling for position, forging alliances and re-aligning their strategy.
Daimler plans to work with Ford and Nissan to produce a commercially-viable fuel cell engine for road-vehicle use. Series production is slated for 2017. BMW and Toyota also recently announced a tie-up, with 2020 as the estimated market entry date.
Toyota has been limbering up for some time to present the world's first production car driven by hydrogen. The debut has been pencilled in for 2015.
Toyota sees the hydrogen fuel cell car as a bold new way forward to go beyond petrol-electric hybrids such as the company's Prius or all-electric cars driven solely by batteries.
The first 10 000 Toyota fuel-cells cars will be based on the FCR-V concept which broke cover at the 2012 Geneva car show. The car is likely to cost some €100 000 and most technical details are still under wraps.
Hydrogen is generally stored in tanks as a liquid cooled to -273°C or else as a highly compressed gas.
"Deep-freezing the hydrogen uses up too much energy," said a Toyota spokesperson, Dirk Breuer. On top of that the tank is empty after a few days because the liquid becomes gaseous and leaks out through safety valves in the system.
"Using a pressure of 700 bar, the lifetime of the fuel is comparable with that of conventional fuels and none of the hydrogen escapes," said Breuer.
Such operating advantages are well-known in automotive research and development departments. Toyota has been working on related projects since 1991.
In 2011 Mercedes-Benz sent its B-Class-based F-Cell car on a trip around the world. The car has been produced in small numbers since 2009. The company says its plans have now gathered such pace that 2017 is a realistic production starting date.
"We've skipped the interim phase," said Daimler research chief Thomas Weber. "We believe that 2017 is the window of opportunity which will allow us to achieve a reasonable sales volume."
Honda has already begun leasing hydrogen-power cars, albeit only in the US and Japan. In 2008 the manufacturer hailed the FCX Clarity as the world's first fuel-cell, hydrogen-powered car.
Now Nissan is planning to team up with Daimler, the company which makes Mercedes-Benz-badged cars, to make a fuel-cell driven SUV based on the Terra concept.
The downside with hydrogen is that it does not occur naturally in the form needed for fuel, and producing it devours a lot of energy. "Most hydrogen is currently produced from natural gas," said Honda in a statement.
Hydrogen made this way is not as green as it might seem.
Fortunately, hydrogen can also be produced from water, although to ensure green credentials regenerative electricity must be harnessed.
Volkswagen is currently putting a fleet of Tiguans through its paces in the US and Germany, although the hydrogen Tiguan HyMotion is unlikely to hit showrooms before 2025.
That is partly because of the lack of a hydrogen refuelling infrastructure, something which will hold back the introduction of such cars in Europe.
The Clean Energy Partnership (CEP), an umbrella organisation for companies from the energy, oil and car sectors, plans to boost the number of refuelling stations in Germany to 50 by 2015.