Fuel cell life span has been getting better, and costs can come down if built in enough quantities. Then it is back to building infrastructure and who pays for that, plus supports it until the cars come.
The composite tanks have an extremely predicable worst case wear pattern that is more to do with cycle wear damage and less aging. If for example if hydrogen tanks at EOL be reused for CNG you could get another 15 years+ out of the tank due to the extremely low pressure. Other possibilities would be a mechanism of communicating the age of the tank and software limit the fill pressures lower and lower after the 15 year date. Other parts of the world could do this but we never think about reuse and recycling streams
Part of it is liability. Another is supply. You need enough hydrogen tanks heading to the dump to make it worthwhile for a company to gather them up, and supply them to the CNG fleet at a price that doesn't just have the fleet stick with the 25yr CNG tanks already available. It's something to pursue when hydrogen cars really start getting on the road. The car makers might have to adopt standardized tank shapes for it to work. Right now, they are using tanks designed to make best use of space, and that might mean they aren't the best fit for a CNG truck. For smaller CNG vehicles, the weight difference may not be desirable.
I believe that both CNG and Hydrogen Tanks have a 15 year recertification process. Most Mirai still have 10 years to go before we know exactly what that means. The Fuel Cell has already been proven to be highly reliable, with one Mirai that I am aware of that has past 200,000 miles. Battery Life should be no different than with a Prius with life span of 10 years to 15 years. The cost should be the same as for a Prius, as its a very similar set up.
Life span depends on the tank type. I've seen Type 4(all composite carbon fiber) CNG tanks listed for 25 years. Would I have heard of recertification is that it generally isn't worth the cost. Fuel cells don't just die, but their output drops. The target for reliability is an average loss of no more than 10% after 5000 hours; IIRC that equals 150k miles in a car. The gen1 Mirai had not reach that. Of course, being an average means some cars didn't see that loss.
It might come sooner than later. Within the last year or two, there's a bunch of Gen 1 Mirais put into ride sharing service (Lyft IIRC) so they might accrue the mileage sooner than the average owner.
That will rack up the hours. A fuel cell is like a battery; there are multiple factors that contribute to degradation. Like batteries, some will last shorter or longer than others. Over an ICE car's lifetime, the engine may lose something like 3% of its output to wear, for comparison.
There has been no reports of noticeable lose of power from anyone within the Mirai Groups, there has been several high mileage vehicles going 150K miles plus. I don't think degradation is a big concern.
"FCEVs have made steady progress toward the DOE MYRD&D 2020 target of 5,000 hours with less than 10% loss of performance (with an ultimate target of 8,000 hours at 10% loss of performance). This performance loss is characterized by the point at which 10% voltage degradation occurs when a new fuel cell stack enters service. Fuel cell power systems must be equivalently durable and reliable to compete with internal combustion engines; therefore, a target of 5,000 hours was chosen as it is equivalent to approximately 150,000 miles of conventional vehicle driving range. It is important to note that the DOE voltage degradation targets are not necessarily representative of what vehicle OEMs or industry consider end of life performance. ... A fairly linear relationship indicates that fleet average hours of fuel cell operation may be a good predictor of overall fleet voltage drop. The data shows for the average fleet projection that 10% degradation occurs at approximately 2,000 hours and approximately 30% degradation occurs at 5,000 hours." https://www.nrel.gov/docs/fy19osti/73011.pdf (pdf) Those results are based on the earlier FCEV fleet; the Mirai was too new. A more recent data point published in 2020 is 4100hrs for the 10% loss point. https://www.energy.gov/sites/prod/files/2020/07/f77/hfto-progress-fact-sheet-june-2020-1.pdf Maybe the gen2 Mirai's fuel cell hits the 5000hr point. It is also something the driver may not notice as the battery is an energy buffer between the accelerator pedal and fuel cell.
