Metal−air battery technology is a promising new energy storage solution in the green energy economy but also an excellent tool to educate students on the working principles of batteries. A simple yet powerful construction of a metal−air battery is shown, which consists of a plastic mint box, a cathode, an anode, and an electrolyte. Furthermore, two different battery constructions are shown, which are suitable for shorter and longer time scales, respectively. Different variables impacting the performance of constructed batteries such as its design and electrolyte composition are demonstrated. The performance figures and efficiencies of assembled aluminum−air, zinc−air, and magnesium−air batteries are compared. Diluted electrolyte is proposed for higher safety.