Energizer 321 Silver Oxide Coin Battery

This is the Energizer 321, a silver oxide button cell sold on its own rather than in a strip. The number is stamped into the top face and the cross marks the positive side, the face that meets the sprung contact in most holders. Silver oxide is the chemistry small watch movements were built around: it holds close to a flat 1.55V for almost all of its working life instead of sagging steadily, so a quartz movement runs at the same rate near the end of the cell as it did at the start.

Cells in this format sit behind the back plate of a wristwatch, and in slim clocks, key fobs, digital thermometers and small calculators. The reliable way to buy the right one is to read the code off the cell you are taking out: button cells that look alike on a counter can differ in height by a fraction of a millimetre and will not seat in the wrong holder. If the old cell reads 321, this is its replacement.

We price and sell this cell singly, so the price on the page buys one 321. The minimum order is ten, sold in multiples of ten, which suits a repair bench, a jeweller's counter or anyone who changes watch batteries often enough to keep a drawer of them. Store spares in their packaging at room temperature, and keep loose cells away from keys and coins, because a button cell bridged across both faces will discharge. Cells of this kind belong out of reach of small children. Other Energizer coin cells sit alongside this one, including lithium CR2032, CR1216, CR1220 and CR1225, and alkaline LR44 and LR54.

What does the number 321 mean, and can I fit a cell with a different code?

It is the cell's own size designation, stamped into the metal. Match it exactly to the cell you are removing, because a different code means a different diameter or height and it will not seat correctly in the holder.

Is silver oxide better than an alkaline button cell of similar size?

For timekeeping, yes. Silver oxide holds a nearly flat 1.55V through most of its life, while an alkaline button cell drifts down in voltage as it drains, which small movements and displays are less happy with.

How many cells do I actually receive?

One. This listing is priced and sold per cell, and the minimum order is ten, sold in multiples of ten, so the smallest purchase brings you ten individual 321 cells.

Which way round does it go in?

The flat printed face carrying the plus sign is positive. In most holders that face sits upward against the clip or cover, but follow the polarity marking moulded into your device's battery compartment.

Is a shelf life printed on this cell?

The manufacturer does not state one for this cell, so we quote no figure. Keep spares in their packaging at normal room temperature and away from other cells and loose metal.