Roundtrip efficiency for batteries are 70-95% vs 47% for H2.

https://www.sciencedirect.com/topics/engineering/round-trip-...

Roundtrip efficiency is not the reason to use hydrogen for anything.

Do you know what’s the (current practical and maximum theoretical) roundtrip efficiency of hydrocarbons (gasoline, alcohol, methane, ...)? Could be a better alternative than H2 (and longer lasting than batteries, even if lower efficiency).

Elektrolysis isn't very efficient, neither are fuel cells, when you compare it to batteries. On top of that you have the energy usage for transporting and most of all compressing the hydrogen for storage.

Bear in mind -- a fueling infrastructure includes a lot of potential points of inefficiency outside of the chemical conversions that are taking place during generation and consumption.

Your fuel of choice also must be transmitted from the point of generation to the point of consumption. For electricity, this is easy, you can run it down a wire. For gasoline, you need a tank that can hold liquid. For hydrogen, you need to cool it to −253°C and compress it in a cryogenic tank.

And water scarcity is expected to be a growing issue for many parts of the world. I guess we could use sea water, but then the shipping you mention comes into play.

Just a side note, you could ship it in hydride tanks.