The shift toward next-generation energy storage is essential for supporting a renewable-heavy grid, where lithium-ion batteries excel in short-duration, high-power applications but struggle with high costs for long-duration needs, resource constraints, material degradation over thousands of cycles, and supply chain vulnerabilities. Mechanical batteries and gravity systems provide robust alternatives by storing energy through physical means—gravitational potential, kinetic rotation, or compressed air—rather than chemical reactions. These technologies deliver exceptional longevity (often 30–50+ years), minimal degradation, high cycle life, and lower environmental impact, making them ideal for grid-scale, multi-hour to multi-day storage to balance intermittent solar and wind generation. Gravity energy storage converts surplus electricity into gravitational potential by raising heavy masses, then regenerates power as they descend. Pumped hydro remains the benchmark, with 70–85% round-trip efficiency and decades-long lifespans, but new solid-mass innovations overcome site limitations. Tower-based systems, such as those from Energy Vault, use cranes to stack composite blocks (often recycled materials) into structures; excess power builds the tower, and controlled lowering drives generators. By 2026, Energy Vault’s Rudong project in China demonstrates commercial viability, with ongoing expansions including hybrid gravity-battery facilities in Texas and Australia, plus licensing deals for regions like Southern Africa. Underground variants, led by Gravitricity, repurpose mine shafts with suspended weights for rapid-response power (seconds to hours), offering modular 4–8 MW scales and near-zero degradation. Flywheel systems store kinetic energy in high-speed rotors (carbon-fiber composites in vacuum with magnetic bearings), achieving 90%+ efficiencies and near-instantaneous response for frequency regulation and renewable smoothing. While suited to shorter durations, advancements push higher capacities and grid integration. Compressed air energy storage (CAES) compresses air into caverns or vessels, expanding it through turbines for longer discharge, with modern variants improving heat recovery for better efficiency. These mechanical solutions promise economic advantages: abundant materials reduce costs (potentially below $100/kWh for long-duration), support circular economies, and avoid fire/chemical risks. They enable higher renewable penetration by minimizing curtailment and replacing fossil peakers. Challenges include lower energy density (requiring larger footprints), site-specific needs, and initial capital, but 2026 sees accelerating deployments, surging investments, and market growth as grids demand reliable, affordable long-duration options. Ultimately, mechanical and gravity storage diversifies beyond lithium, harnessing simple physics for resilient, sustainable energy systems that ensure abundance and security in the renewable era.