Renewable energy storage is key to addressing the intermittency of wind and solar power. Pumped hydro, which stores excess energy by moving water to higher altitudes, dominates global storage but is costly and geographically limited. Lithium-ion batteries are increasingly popular due to falling prices and larger storage capacities, though they face challenges like degradation, safety risks, and recycling issues. Emerging technologies like solid-state batteries promise improvements but are still far from market-ready. International standards ensure the safety and efficiency of these systems while paving the way for future innovations.