With the clean energy revolution, many methods of energy production, such as solar and wind power, are quite unstable because of weather variability. However, energy consumption remains relatively stable. Therefore, efficient energy storage could be crucial for the future. In this context, we will explore the theoretical limits of battery efficiency in terms of energy density. Surprisingly, although quite speculative, a potential solution might involve a cellular battery composed of micro black holes. In fact, let us suppose hypothetically that advanced future technology can handle the formation of black holes. Then, according to the extremal solution of the Reissner–Nordström metric from general relativity, such a battery could be stable and would not collapse into a larger black hole because the electromagnetic repulsion would precisely offset the force of gravity. Additionally, although it is generally assumed that nothing can escape from a black hole, a micro black hole could possibly annihilate another micro black hole, resulting in the release of an enormous amount of clean energy. For example, a battery weighing just one kilogram could provide approximately 470 million times the energy of the most efficient 200-kilogram lithium battery at the time of writing. While achieving such a level of technological advancement is certainly not imminent, it is not inconceivable that battery technology development could follow a trajectory similar to that of computer technology. Just as breakthroughs in physics and computer engineering have led to exponential growth in computer efficiency in the last 50 years, it is possible that battery efficiency could double or even quadruple every few years following different types of breakthroughs. Nonetheless, the theoretical concept of a micro black hole battery appears to align with current predictions of fundamental physics regarding the ultimate physical limits on energy density storage. This strongly indicates we are at the very early stage of battery technology, not even close to the end.