South Korean secondary battery stocks rebounded sharply as large-cap semiconductor shares corrected, with investors citing oversold conditions and a shift in U.S. policy toward treating energy storage systems (ESS) as critical equipment for the power grid and national security. From Aug. 21 to Aug. 28, Samsung SDI rose 19.5%, LG Energy Solution gained 7.7%, POSCO Future M advanced 20.3%, EcoPro BM increased 11.9% and L&F surged 29.0%, while Samsung Electronics and SK hynix fell 8.7% and 4.5%, respectively. The United States declared a national emergency over the bulk-power system on Aug. 26. The regulatory scope includes transformers, generators, battery energy storage systems (BESS), grid-tied inverters, uninterruptible power supplies (UPS) and related software, while foreign equipment considered a national-security risk could face restrictions on new purchases, imports and installation. The move may make local production, supply-chain reliability and cybersecurity more important than price in the U.S. ESS market, where Chinese manufacturers have strong cost advantages. North American ESS demand reached 75.9 GWh in the first half, up 83% from 41.5 GWh a year earlier, while the combined market share of two Korean manufacturers rose to 19.7% from 13.9%. Samsung SDI also remains a focus of institutional investors, with approximately 502.8 billion won in net purchases through Aug. 28 and a roughly 50% monthly share gain, supported by expectations for solid-state battery mass production in the second half of 2027, ESS growth and investment in AI data-center power systems. Analysts caution that the rally will need to produce actual ESS orders, higher utilization rates and improving quarterly earnings to become more than sector rotation.