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Grid-scale battery storage has moved from a niche engineering concept to a central component of electricity system planning over the past decade, as the share of power generated from intermittent renewable sources such as wind and solar has climbed steadily in many national grids. The fundamental challenge these renewables pose is not one of total output but of timing: solar panels generate no electricity after sunset and wind turbines produce power according to weather patterns rather than demand, creating mismatches between when electricity is generated and when it is actually needed by homes and businesses. Large lithium-ion battery installations, often built alongside solar or wind farms, address this mismatch by storing surplus electricity generated during periods of high output and releasing it during evening peaks or periods of low wind, effectively smoothing supply to match demand. Grid operators have reported that regions with substantial battery capacity experience fewer instances of price spikes during demand peaks, since stored electricity can be dispatched instead of relying on expensive backup power plants that are otherwise kept idle for exactly these moments. The cost of battery storage has fallen sharply, driven largely by manufacturing scale-up for electric vehicles, which has made grid-scale projects increasingly competitive with traditional peaking power plants fuelled by natural gas. Nonetheless, meaningful limitations remain. Current battery technology can typically discharge stored power for only a few hours before depletion, making it well suited to daily supply-demand smoothing but poorly suited to covering prolonged periods of low renewable output that can last several days during unfavourable weather. Engineers and policymakers generally view battery storage as one part of a broader portfolio that must also include transmission upgrades, demand-response programmes, and, in many proposed grid designs, longer-duration storage technologies still in earlier stages of commercial deployment.