Lithium-ion batteries are the most widely used rechargeable energy storage solution, powering everything from smartphones and laptops to electric vehicles and renewable energy grids. Known for their high energy density of around 250–300 Wh/kg, they provide an excellent balance of power, efficiency, and compact size. Each cell operates within a voltage range of 3.2 to 4.2 volts, delivering strong and consistent performance. With a typical lifespan of 1000–2000 charging cycles, lithium-ion batteries can last 3–7 years depending on usage. They are lightweight compared to older technologies such as lead-acid batteries, which makes them ideal for mobility solutions like EVs. Advanced battery management systems (BMS) ensure safe operation by regulating charging, preventing overheating, and extending battery life. Fast-charging technology further enhances their usability, enabling recharges in as little as 1–2 hours. While recycling and environmental concerns remain challenges, advancements are being made to improve sustainability. Their ability to store renewable energy from solar and wind power makes them crucial for clean energy transitions. Affordable, efficient, and widely available, lithium-ion batteries are currently the backbone of modern portable electronics and electric vehicles, and they continue to evolve with ongoing innovations in chemistry and manufacturing.