A device that stores energy chemically and releases it as electric current — from Volta's pile of 1800 through lead-acid and lithium-ion cells to grid-scale storage — and now the linchpin of mobile technology and the renewable-energy transition.
Electricity has one crippling weakness: it is hard to store. You can send it across wires almost instantly, but a grid has to balance what it makes against what it uses moment by moment — it cannot easily save power now to release later. The battery solved part of that. It stores energy chemically and releases it as electric current on demand. That trick — first achieved with a stack of silver and zinc discs in 1800 — made chemistry talk to physics, gave science its first steady current, and eventually put a phone in your pocket and threatened to make the fossil-fuel century obsolete.