Coin & Button Cell Batteries

Which button cell battery do I need?

Our advice is to start with the old cell. Its code is printed on a flat face, usually the side marked with a plus sign, and it tells you both the chemistry and the size. If the print has rubbed off, the device's manual or the inside of its battery cover will often show it. Match the whole code, letters and numbers together, because cells that look alike can differ in thickness or voltage.

Check, too, whether the device takes a single cell or a short stack, and whether the old cell had wire leads or metal tabs, as you may find inside a computer; a tagged cell needs a like-for-like replacement.

How to read the code on coin and button cell batteries

The letters come first. On codes that follow the international standard, C stands for lithium, L for alkaline and S for silver oxide, and the R that follows means the cell is round. On lithium coin cells the digits are a measurement: the first pair usually gives the diameter in millimetres and the rest gives the thickness in tenths of a millimetre, so the code doubles as a size guide.

Button cell codes are less tidy: their numbers can be a reference rather than a measurement, and the same cell can be sold under different names, so a pack may list alternative codes. Letters added at the end usually mark the type, such as a higher-drain version, rather than a different size.

What is the difference between coin and button cell batteries?

The names overlap, but as a rule a coin cell is wide and thin, like a coin, and usually lithium, while a button cell is smaller across, thicker for its size and usually alkaline, though many are silver oxide. Coin cells tend to sit in key fobs, scales and motherboards; button cells turn up in watches, calculators, thermometers and small toys. Shape alone is not enough to go on, so let the code decide.

Does the chemistry of a button cell battery matter?

Yes, because chemistry sets the voltage. A lithium coin cell runs at roughly twice the voltage of an alkaline or silver oxide button cell, so one should not stand in for the other, even where the sizes look close. Lithium coin cells also keep their charge for years in a drawer, which suits key fobs and computer clocks.

Between the button cell types, silver oxide holds a steadier voltage until it is nearly spent, which is why watches usually call for it. An alkaline cell of the same size will usually fit and work, but it runs down sooner, so it suits simple, low-drain gadgets better than a good watch.

How to fit a coin or button cell battery

Before you lift the old cell out, note which way up it sits: the side with the plus sign and the printing usually faces you, but devices vary. Hold the fresh cell by its edges, keep metal tweezers from touching both faces at once, and press it in until it sits flat under its clip. Switch off and unplug a computer before changing its motherboard cell.

Expect to set the time again on a watch or a computer afterwards. If a car key stops responding after a battery change, the vehicle handbook will say whether it needs pairing again.

Storing and recycling button cell batteries

Keep spare cells somewhere cool and dry, away from loose coins and keys that could short them, and out of the sight and reach of children. A swallowed coin or button cell can cause serious internal injury within hours, so if you think a child has swallowed one, take them to A&E at once. After changing a cell, check that the battery cover is secure.

Used cells can still hold charge, so keep them out of the household bin. Tape over both faces of a used lithium coin cell, then take your spent cells to a battery recycling point; supermarkets and household waste recycling centres usually have one.