[anovikov]

LOL energy density is much much lower, but volumetric density is several times higher. Meaning, they take less space for same weight -> airframe can have smaller profile and have less air resistance.

[kgabis]

I don't think that's true, both volumetric and mass densities for lithium ion batteries are very low (https://upload.wikimedia.org/wikipedia/commons/c/c6/Energy_d...).