Well we know gasoline as an organic battery is 50x more energy dense than an EV battery by weight for example and 25x more dense by volume.

And if you want to get really exotic, antimatter is about 83.2 billion times more energy dense. We're not going to be running into fundamental physics limitations for energy storage anytime soon.

Though maybe it's a little unfair to call either of those things a "battery", they seem like fundamentally different technologies to me even if in theory they could fill exactly the same role.