Aqueous metal batteries represent a compelling avenue for energy storage solutions. Currently, research efforts are heavily concentrated on period 4 transition metals, starting from the prominent zinc to emerging candidates of iron, nickel, copper, and manganese. However, period 5 transition metals remain underexplored and poorly understood. Herein, we selected an underrepresented cadmium metal and investigated its fundamental plating chemistry, which showcases an unprecedented electrode performance, including low polarization (∼5 mV), long lifespan (4000 hours, 5.5 months), and exceptional plating efficiency. Notably, the efficiency approaches unity (99.92%) at 1.0 mA cm⁻² and 1.0 mA h cm⁻², and it retains 99.60–99.82% in more aggressive conditions (5–10 mA h cm⁻²; 0.25–0.50 mA cm⁻²). Surprisingly, such a performance is achieved without utilizing sophisticated electrolytes, additives, or surface treatments, which likely results from its suitable Cd²⁺/Cd redox potential, high resistance to hydrogen evolution, and densely stacked plate-like morphology. High-energy, high-rate, and long-cycling cadmium batteries have also been demonstrated. Our work contributes novel insights into the design of high-performance metal batteries.