Energy density. There is more energy in a tank of gas than a battery can store electrically.
One of the reasons this is the case is that the reactants in the batteries have to be stored within a vessel (cell). With fuel, the hydrocarbons are actually only half of the reactants, with oxygen being the other part of the chemical equation, and you don’t have to store O2, that can just be taken out of the air to mix with the fuel in real time.
With batteries always containing the reactants needed for energy storage, that also means that failure can cause it to all react at once, so it has to be protected against electrical, thermal and chemical degradation, adding weight and therefore reduced energy density.
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