Button cells are the batteries people most often get wrong, because the codes look similar and the physical difference is fractions of a millimetre.
The code is a size, in disguise
Take CR2032. The letters tell you the chemistry, the first two digits are the diameter in millimetres, and the last two are the thickness in tenths of a millimetre.
So a CR2032 is 20mm across and 3.2mm thick. A CR2025 is the same 20mm across but only 2.5mm thick, which is enough of a difference that it may not make contact or may not fit the holder at all.
| Code | Chemistry | Size | Typical use |
|---|---|---|---|
| CR2032 | Lithium | 20 x 3.2 mm, 3 V | Key fobs, scales, motherboards, sensors |
| CR2025 | Lithium | 20 x 2.5 mm, 3 V | Slim remotes, small wearables |
| CR2016 | Lithium | 20 x 1.6 mm, 3 V | Slim watches, some fobs |
| CR2450 | Lithium | 24.5 x 5.0 mm, 3 V | Keyless entry, tyre sensors |
| LR44 | Alkaline | 11.6 x 5.4 mm, 1.5 V | Toys, small torches, calculators |
| SR626SW | Silver oxide | 6.8 x 2.6 mm, 1.55 V | Wristwatches |
CR versus LR versus SR
CR means lithium manganese dioxide: 3V per cell, long shelf life, good in the cold. LR means alkaline: 1.5V per cell and prone to leaking. SR means silver oxide: 1.55V and very stable, which is why watches use it.
LR and SR cells of the same diameter are physically interchangeable but not electrically identical. A watch that expects silver oxide will run, then keep poor time on alkaline.
They are never rechargeable
No coin cell is designed to be recharged. Putting one in a charger, or wiring it to a supply, can cause it to vent, leak or catch fire. Replace them.
Buy from a shop with reasonable turnover. A five-pack of unbranded cells from a marketplace may be years old and partly flat before you open it.
The swallowing hazard
A swallowed button cell can cause severe internal burns within a couple of hours, and symptoms may not appear at first. This is a genuine emergency, not a wait-and-see situation.
If you think a child or anyone else has swallowed one, seek urgent medical help immediately: go to A&E or call 111. Do not try to make them vomit. Keep spare cells out of reach and tape both sides of a used cell before binning it, so it cannot cause a burn if it ends up somewhere it should not.
Store coin cells in a child-proof container, not a drawer. A flat cell still carries enough energy to injure. Tape used cells on both faces and take them to a battery collection point.
Buying the right one
Open the device and read the cell itself, not the manual, which may cover several variants. Check the code, the voltage and whether the old cell was lithium or alkaline.
If your key fob has stopped working, test the cell before replacing it: a CR2032 that reads 2.9V may still need changing, because fobs need a firm voltage to transmit.
The short version
- CR2032 is 20mm wide and 3.2mm thick, and the code tells you both.
- CR is 3V lithium, LR is 1.5V alkaline, SR is 1.55V silver oxide.
- Coin cells are never rechargeable.
- A swallowed button cell is a medical emergency. Get help immediately.