From the above:
At its core, a hydrogen car is an electric vehicle with a small onboard battery that is continuously charged from a hydrogen fuel cell that pulls stored hydrogen gas, mixes it with oxygen from the atmosphere, and runs it through a proton exchange membrane, releasing electricity along the way. The only byproduct of this process is water, making the vehicle essentially just an electric vehicle that gets its power from a different type of onboard battery drivetrain. I’ve driven both popular models for CleanTechnica — the Toyota Mirai and the Honda Clarity Fuel Cell — and found that they both drove and operated like “normal” vehicles, which is great.
This article refers to a "small onboard battery" that is continuously charged from a hydrogen fuel cell. This seems a lot better than having a huge weight of batteries that takes ages to charge with electricity. I wonder how long this small onboard battery would last before it needs replacement?
True, but you're replacing a huge weight of batteries with a huge weight of ultra-high pressure gas storage tank. Hydrogen is a slippery wee molecule, and the tanks to hold it need to be stronger and solider than your average LPG cylinder.
Solider? Nice word!! :-)