I think it's generally understood that densities are per unit volume, and if you want to refer to gravimetric density, you would talk about the 'specific energy

I think it's generally understood that densities are per unit volume, and if you want to refer to gravimetric density, you would talk about the 'specific energy.' [0] That said, you make a good point. The energy density advantage isn't huge when comparing to liquid H2, although it's more significant vs compressed H2. [0] https://en.wikipedia.org/wiki/Specific_energy https://en.wikipedia.org/wiki/Specific_energy