"It is not feasible to get much more energy into a material than 1 eV per atom. Most solids have atomic weights of 30 GeV/c^2 [*] which yields E/m = 3x10^-11 c

"It is not feasible to get much more energy into a material than 1 eV per atom. Most solids have atomic weights of 30 GeV/c^2 [*] which yields E/m = 3x10^-11 c^2. When you convert this into the more human Watt-hour/kg, you get 850 W-hr/kg. " https://www.quora.com/Is-it-true-that-battery-energy-density-improves-5-8-per-year-Does-this-represent-an-average-or-is-it-a-consistent-trend-each-year-Do-these-improvements-increase-the-cost-What-has-been-the-trend-if-any-regarding-energy-to-weight-ratio https://www.quora.com/Is-it-true-that-battery-energy-density... I believe.. this is true, but not 100% sure. However the limit is higher with air batteries... as stated in another answer. The energy density of gasoline is high because it uses air intake for oxidation. Also... part of why rockets are so big is because they also don't use oxygen from the atmosphere, they carry their oxidizer in the rocket.