Batteries & cells

A cell is a tiny chemical pump. A reaction inside pushes electrons out of its – terminal and pulls them in at the + terminal, creating a voltage difference between them. A battery is simply one or more cells packaged together — the words are often used interchangeably, but strictly a battery is a bank of cells.

Cell size does not uniquely determine voltage. Common alkaline AA/AAA cells are nominally 1.5 V, rechargeable NiMH AA/AAA cells about 1.2 V, a CR2032 lithium coin cell 3 V, and many lithium-ion cells 3.6–3.7 V nominal. Actual voltage varies with chemistry and charge. A typical alkaline 9 V battery contains six series cells.

Two specs matter when picking a battery: its voltage (does it match what your circuit needs?) and its capacity in mAh (how long will it last?). A higher voltage doesn’t mean it lasts longer, and more mAh doesn’t raise the voltage — they’re independent.