The use of electrochemical batteries for portable power in consumer electronics, industrial equipment and vehicles has come to be a daily experience for people worldwide. The most popular battery types are the lithium-ion batteries, which have been the dominant form of energy storage in portable electronic devices such as computers and mobile phones over the last two decades, and the lead-acid batteries, which are used in internal-combustion vehicles to provide the initial current to engine starter motors. Nickel-metal hydride batteries come anywhere near to lithium-ion across key performance parameters such as energy density, power density, charge time, life cycle and safety, and are used in niche applications where energy density is less critical. Continues technical improvements brought lithium-ion batteries into new markets beyond portable electronics. Market solutions for both electric vehicles and electricity storage, whether grid-connected or installed behind-the-meter (i.e. in a home or at a business), are already commercially available. These technologies are finding success in profitable niches, such as electric bicycles, scooters and motorcycles, passenger cars, and uninterruptible power supplies in data centres. Solid-state lithium-metal batteries, long considered “the holy grail” of lithium-ion battery technology, have now moved from the realm of theory into reality. These next-generation batteries offer large non-marginal improvements over existing battery technology in terms of energy density, battery durability and safety, while also enabling charging times that are extremely rapid by today’s standards. Going beyond the all-solid-state lithium battery, breakthroughs in lithium-air technology might provide a similar step change in the energy density available from batteries. The market for energy storage batteries points towards a need for longer lifetimes, better performance across a range of temperature conditions, and lower per unit costs. Lithium-ion batteries are already cost competitive and used for grid electricity storage in a range of markets, and, in the near future, so-called flow batteries may also emerge as stiff competition for lithium-ion batteries. Flow batteries have a much lower energy density than lithium-ion batteries, and as a result are much heavier and bulkier by comparison. However can discharge and provide power for as much as 10 hours and have very long lifetimes (30+ years), and do not use flammable electrolytes, making them potentially safer to operate. Any future advances in battery technology beyond current technologies have the potential to rapidly accelerate the deployment of electric vehicles and renewable electricity generation. Battery storage systems are emerging as one of the potential solutions to increase the flexibility of variable renewable energy system, due to their unique capability to quickly absorb, hold and then reinject electricity.