Check the article link below for a chart starting with ENIAC
The researchers found that the electrical efficiency of computing has doubled every 1.6 years since the mid-1940s. “That means that for a fixed amount of computational power, the need for battery capacity will fall by half every 1.6 years,” observes Dr Koomey. This trend, he says, “bodes well for the continued explosive growth in mobile computing, sensors and controls.” Some researchers are already building devices that run on “ambient” energy harvested from light, heat, vibration or TV transmitters. As the energy-efficiency of computing continues to improve, this approach will become more widespread. Dr Koomey’s team published their results in IEEE Annals, an industry research journal. Inevitably, industry observers are already calling this new finding “Koomey’s law”.