A LiOn battery is good for many many cycles, and can then be recycled. Hydrogen must be produced and then consumed, and is usually produced from natural gas, itself a greenhouse gas that is on the main a byproduct of the oil industry.
The proof is in the pudding: the curb weight of a Mirai is more than that of the larger and more capable Model 3.
Although, after google search, I see that the Mirai weight is 4075 lb, and the Prius weighs around 3100 lb.
Maybe there's a future world in which we can do it all in orbit -- harvest comets, produce hydrogen in space using solar power or nuclear, and efficiently drop it down to earth in some safe way. That would definitely alter the equation. But by the time we figure that out, it'll probably be too late.
Personally I don't going into competition with laptops, mobile phones and car battery manufacturers as a viable long term strategy for grid scale storage.
Any electric car plugged in is a great buffer for surplus electricity production.
Taking the number above for installed capacity of pumped hydro. You are looking at nearly half a million cars and homes to match the capacity (assuming 50kwh per vehicle), before considering the plugged in factor.
At say a nice round £1000 to upgrade each home you are already looking at a cool half a billion. Already around the cost of the Dinorwig pumped hydro station before you figure out how to compensate electric car owners for the extra wear on their batteries or the fact that when they leave for work their car is flat because it has been powering your neighbors electric showers.
https://about.bnef.com/blog/hydrogen-economy-offers-promisin...
Pretty much all battery research is targeting materials that are common. The DoD made a large bet on Lithium-Sulfer batteries.
Battery recycling can be energy intensive if you go for the full metallurgical extraction. But pretty much all car manufacturing plants want to just 'disassemble' the battery and use other far less energy intensive processes to get battery grade materials out. Also, at least in the west, these factories are generally located in location where there is cheap green energy or at least there is the potential. That is both Tesla/Panasonic and Northvolt (Europe) plan.
With batteries you can reload the battery from your gravitational energy. That is actually quite a significant range extender but it might be a regulatory issue.
But hydrogen requires production, either from fossil fuels, or electrolysis, both can be environmentally taxing. It requires transport. It requires either liquefaction or compression. It require mining to manufacture suitable storage tanks - which will become brittle and have to be replaced pretty often.
> Hydrogen also depletes along the trip unlike battery which will be massive dead weight for planes & ships.
This is indeed a major difference.
Frankly, if you want to burn hydrogen, you're better off synthesizing something like methane. It's a far more effective storage mechanism. After all, if you are willing to spend the massive amount of resources required to do large-scale electrolysis, you might as well go the extra step and setup some sabatier reactors. You'll recapture the CO2 too.