Which coin cell is this, and what else is it sold as?

2Reading the code

Two letters, then digits. The letters are the chemistry, and every maker’s datasheet pairs them the same way: CR is lithium manganese dioxide at 3 volts, BR is a cousin lithium chemistry at the same 3 volts and the same sizes, LR is alkaline at 1.5, SR is silver oxide at 1.55, PR is zinc air at 1.45 for hearing aids. The digits are the size. No maker writes the rule out in a sentence, but every table they print lines up the same way: 20.0 by 3.2 millimetres beside CR2032, 20.0 by 2.5 beside CR2025, 6.8 by 2.6 beside SR626, 9.5 by 2.0 beside SR920. Width first, then thickness in tenths. The exception is the two-digit button cells, LR44, SR44, LR41, SR43, where the number is just a number from an older list: an LR44 is 11.6 across and 5.4 thick, and nothing about 44 tells you that.

A silver oxide watch cell comes in two versions of every size, and the letters on the end say which. Maxell’s wording: the low-drain type, SW, for things that run a long time on a light load, an analogue watch; the high-drain type, W, for things that pull short heavy loads, a digital watch with a backlight and an alarm, a stopwatch, medical kit. Energizer says the same in chemistry: sodium hydroxide electrolyte for the low drain, potassium hydroxide for the high. The three-digit codes split the same way, so a 377 is an SR626SW and a 376 is an SR626W. Same cell to look at. Buy the one the watch had in it.

3DL, ECR, V, AG and the three-digit numbers

DL is Duracell’s prefix: its own page says a Duracell 2032 is ‘equivalent to DL 2032, CR 2032’, which is a maker telling you its name and the standard name are one thing. ECR is Energizer’s, and Duracell’s UK pages print a table of them, industry name, Energizer name, Varta name, Panasonic name, four columns for one battery. V is Varta: V13GA for the LR44, V357 for the 357. The three-digit numbers, 357, 377, 364, 392, are the watch trade’s, from before the IEC codes, and Renata’s cross-reference chart lines them up against ten makers, with Seiko’s SB- codes and Citizen’s 280- codes alongside for anyone taking a watch back apart. AG13, SG13 and the rest of the AG numbers are the cheap packs’ own system and the big makers don’t print them, with one exception: Energizer lists AG13 and SG13 among what its A76 replaces, which is the only place on a maker’s page you’ll find them admitted to.

4Alkaline or silver in the same hole

An LR44 and an SR44 are the same 11.6 by 5.4 millimetres, and Energizer’s page lists the 357, the 303 and the SR44 among what its alkaline A76 replaces, so one goes where the other was. They are not the same battery. Silver oxide sits at 1.55 volts and holds it to the end; alkaline starts at 1.5 and sags as it goes. A watch wants silver, and Maxell files every SW cell under analogue watches and thermometers for that reason. A toy, a calculator, a laser level or a kitchen thermometer is fine on alkaline, and alkaline is what the big packs are. If the thing has a watch movement or a meter in it, pay for the silver. If it has a motor or an LED in it, don’t.

5Thickness is the fit

Energizer prints the same warning on every coin cell page: coin lithium batteries are not interchangeable, the diameter and the thickness both vary by designation, a compartment may be sized so that a different cell fits, and you should use the one the device maker specified. That’s the CR2032 and CR2025 problem in a paragraph: same 20 millimetres across, 0.7 of a millimetre apart in thickness, the thin one rattles in the fat one’s holder and loses contact on a bump, the fat one won’t let the case shut. The key fob sheet has four of them drawn in section. Match the last two digits.

6Children

The Child Accident Prevention Trust’s page is short and worth the minute. A button battery can badly hurt or kill a small child who swallows one, and it looks like a sweet. If you think a child has swallowed one, go straight to A&E or call an ambulance; don’t wait for symptoms. Keep the spares up high and out of reach, and get rid of the dead ones the day they come out, because a flat cell is still dangerous. The 20 millimetre lithium coins on this sheet are the ones the child-safe packaging is for. Buy the packs that make you cut the card.