How AA batteries are made

An alkaline cell is zinc powder, manganese dioxide and potassium hydroxide in a steel can.

stations: 8
things upstream: 75
raw sources: 22
steps from the ground: 10

The short version

The can itself is part of the positive electrode. Manganese dioxide, carbon and potassium hydroxide are mixed, granulated and pressed into hollow rings that slide into a nickel-plated steel can. A paper separator lines them, a zinc gel fills the middle, and a brass nail through a plastic seal collects current from the zinc. The result gives 1.5 volts.

Mix the cathode

Trainloads of manganese dioxide, carbon and potassium hydroxide solution are mixed in very large batches at the plant, then granulated.

Goes in
Manganese Carbon black Potassium hydroxide Water
Press hollow rings

The granules are compacted into hollow cylinders called preforms, and several may stack in one cell. Some makers extrude a single ring of the same material instead.
Form the steel can

Large operations cut and form their own nickel-plated steel cans. The preforms are pushed in, and the can and rings together become the positive electrode. A groove near the top gets a sealant to stop leaks.

Goes in
Steel Nickel
Line with separator

Several pieces of paper, laid crossgrain like plywood and soaked in electrolyte, go in like a paper cup. This keeps the two electrodes apart. Some designs use a porous synthetic fiber.

Goes in
Paper
Fill with zinc gel

A very thick paste of zinc powder and electrolyte goes in the center. It stops short of the top, leaving room for the chemical reactions in use.

Goes in
Zinc Potassium hydroxide
Crimp in the seal

A brass nail welded to a metal end cap passes through a plastic seal and reaches about two-thirds of the way down into the gel. The seal has thin spots that rupture first if gas builds up, and it is crimped into the groove.

Goes in
Brass Plastic
Close the positive end

A steel plate is welded or glued with an epoxy-type cement over the opposite end of the can, which becomes the battery's positive terminal.

Goes in
Steel
Label and test

A glued paper label or a loose plastic sleeve goes on, and a blast of heat shrinks the sleeve tight. Ingredients and cells are checked at almost every stage, and finished batches are tested hard.

Goes in
Plastic wrap

End of the lineAA battery

Worth repeating

Lewis Urry invented the modern alkaline dry cell in the 1950s.
An AA alkaline cell might give 3,000 mAh at a light load but as little as 700 mAh when delivering 1 ampere.
In the mid-1980s, alkaline batteries commonly held five to seven percent mercury, added to fight corrosion until purer ingredients replaced it.