Why does a battery weaken in the cold?

Teacher’s note

The question is meant to show the cell of target 5, ions inside, electrons outside, and that cold hinders only the former. Copper, for its part, conducts better cold, 0.4% per degree. The ions slow down: in the electrolyte, the organic carbonates of lithium-ion or the potassium hydroxide paste of the alkaline, which thickens; then at the interface, where the electrode reaction follows Arrhenius. An alkaline AA gains 40% resistance per ten degrees colder; lithium-ion, little down to 0 °C, a lot below.

Open-circuit voltage is the chemistry’s promise, nearly untouched by cold. Internal resistance is how fast it keeps that promise. Hence the diagnosis of target 7, which movement of charge is hindered, and where: not the electrons, the ions; not the wire, the electrolyte and its surface.

The measurement that settles it: open-circuit voltage, then voltage under load, the difference divided by the current. At rest, the probes reach the pack’s blades; under load, the tool covers them: you need an adapter, two thin copper strips between pack and tool, with a loop of wire for the clamp meter. The meter’s MIN/MAX catches the start-up peak; otherwise, steady state, impeller unloaded, 10 to 15 A. Without an adapter, the sister experiment proves it on a single 18650.