The number of battery chemistries that check the boxes of high specific energy (>100 W h kg^–1), rechargeability, power performance, inherent safety, low cost, and worldwide abundance is a short list. While lithium-based batteries continue to permeate the energy-storage landscape, many safety and supply concerns remain. Aqueous-electrolyte batteries meet many of the requirements for next-generation energy storage devices, but depending on the chemistry (Pb acid, Ni–MH, Ni–Zn, Zn–Air) often fail when it comes to safety, specific energy, and/or rechargeability. The radar chart below reveals the advantages and disadvantages of several battery technologies and especially highlights that improvements to rechargeable Zn-based batteries will propel them to the forefront of the energy landscape. The historical hindrance to broader use of Zn-based batteries is the poor rechargeability of the Zn electrode, especially when formulated as a powder-bed electrode that is too prone to launch dendrites upon cycling, which then short-circuit battery operation. The U.S. Naval Research Laboratory has redesigned the Zn electrode into a monolithic, metallically interconnected three-dimensional sponge form factor that supports a more uniform current distribution, thereby allowing nearly complete utilization of the Zn active material (>90%; projecting to ~450 W h kg^–1) and avoiding the local critical current density required to spawn dendrites upon cycling. We established the reversibility of our 3D Zn sponge electrodes by cycling in Ni–3D Zn coin cells with particular emphasis on suitability in next-generation electric and start–stop vehicles. The lessons derived from studying Ni–3D Zn deep cycling allow us to demonstrate preliminary cycling performance of 3D Zn–air cells and offer prescriptions on appropriate electrolytes, current collectors, cell-fabrication particulars, and the future of Zn-based batteries.