Generally a >10x is easily achievable if we use a chemical reaction that uses oxygen - which we do not have to carry around, that's why things like hydrogen fue

Generally a >10x is easily achievable if we use a chemical reaction that uses oxygen - which we do not have to carry around, that's why things like hydrogen fuel cells have a theoretical energy/mass that we can pretty much assume is best possible with a chemical reaction. Unfortunately the problems with hydrogen storage and the fuel cells have prevented them from really taking off.