Is a 377 the same battery as an SR626SW, and can I use a 376?

A 377 and an SR626SW are the same battery: 377 is the Energizer number, SR626SW the size-coded name most other makers and sellers print. The trouble is the word "equivalent". Cross-reference charts match cells by size, and by size alone a silver oxide SR626SW, a high-drain SR626W and an alkaline LR626 are interchangeable. Only the first two are right for an analog quartz watch.

What the Energizer data sheet says about the 377

Energizer publishes one sheet for the 377 and the 376 together, Form EBC-4364B. The copy online is stamped "obsolete", but its figures are the most complete any maker has published for this size:

Two details settle most of the arguments. Energizer prints IEC SR66, not SR626SW, so listings for "SR66" and "SR626SW" describe the same cell; Renata, the Swatch Group's battery maker, prints both on one line, "377, SR626SW (SR66)". And Energizer makes no separate 376: one cell carries both numbers, built for the low-drain and the high-drain job at once.

How to read the name on the packet

The size-coded name can be read without a chart. Set the cells in Maxell's catalog against their dimensions and the pattern is exact:

• SR is silver oxide; LR is alkaline; CR is lithium manganese dioxide.
• The first one or two digits are the diameter in whole millimeters: 6 for 6.8 mm, 9 for 9.5 mm, 11 for 11.6 mm.
• The last two digits are the height in tenths of a millimeter: 26 for 2.6 mm, 20 for 2.05 mm, 36 for 3.6 mm.
• The suffix is the electrolyte: SW for low drain, W for high drain.

The three-digit Energizer numbers and short IEC designations such as SR66 carry no such logic; decoding them takes a table like the one further down.

SW and W: what the suffix changes

Maxell, which since 1 March 2026 also supports the cells that carried the Murata name, explains the split. Its silver oxide cells come in two types "configured according to electrolyte composition": the low-drain SW type uses an aqueous sodium hydroxide solution, the high-drain W type a potassium hydroxide solution.

• SW, low drain: for devices "intended for long-term use at low power such as quartz watches (analog watches)". Maxell rates the SW type at approximately twice the leak-resistant life of its W type.
• W, high drain: for "multifunction digital watches equipped with backlights, stopwatches and alarm functions".

Maxell lists the SR626SW and SR626W at the same 1.55 V, the same 30 mAh and the same 0.4 g. The catalog difference is the nominal discharge current: 30 microamps for the SW, 50 for the W. So a 376 runs an analog watch. You give up leak resistance, not timekeeping, and since a watch cell sits in the movement for years, the SW is the better buy when both are on the shelf. The reverse swap matters more: if the manual of a watch with a backlight or alarm calls for a 376 or SR626W, fit a W.

Why an alkaline AG4 is the wrong swap

An alkaline LR626, also sold as AG4 or LR66, is the same size as an SR626SW. Eurobatt's engineering data sheet gives it as 6.80 by 2.60 mm, and its cross-reference line reads "377, L626, V4GA": the confusion is printed by the manufacturer. Here is how the two compare on their makers' sheets:

The alkaline figure is taken on a heavier load, which costs capacity, but down to 0.9 V, which adds it. Even so it reaches 10 mAh, about a third of the silver oxide rating.

The voltage curve is the bigger problem. Energizer's own alkaline button cell, the LR44-size A76, publishes its voltage by depth of discharge: 1.55 V fresh, 1.33 V at 40 percent of capacity, 1.20 V at 80 percent. Maxell describes its silver oxide cells the opposite way, "operating voltage is stable up to the end of discharge", and Energizer's 377 curve holds a flat line until late in its 795 hours.

A quartz movement watches its supply voltage. ETA's technical communication for its 955.112 caliber, which takes a 2.05 mm cell (a 371), checks normal running at 1.55 V and the end-of-life mode at 1.30 V. That mode is the jumping seconds hand that tells you the battery is nearly flat. A silver oxide cell reaches that voltage near the end of its life, which is the design. An alkaline cell is close to it before half its already small capacity is used, so the warning, and then the stop, come with much of the cell unspent. Other calibers set their own thresholds; this is the one ETA publishes for that movement.

The ten commonest watch cells, cross-referenced

Energizer's sheets give the number, IEC designation, dimensions and rated capacity; Maxell's catalog gives the SW and W capacity at its own nominal current. Where Energizer prints two numbers on one sheet, both are shown.

Compare capacities within a column, never across: Energizer and Maxell measure on different loads. Energizer pairs 395 with 399, 394 with 380 and 390 with 389 as one cell for low drain with high pulses, where Maxell sells separate SW and W versions. The 373 and 379 sheets say "continuous low drain" only, so they are not cells for a watch with a light or alarm. And a shared diameter is not enough: a 364 is as wide as a 377 but up to 0.7 mm thinner on Energizer's tolerances. Go by the number on the old cell or in the manual.

Digital watches and lithium coins

Many digital watches use a 3 V lithium coin instead, most often a CR2016 or CR2025, as in several Casio modules. Both are 20 mm across; the code gives 1.6 mm against 2.5 mm high. Energizer rates the CR2016 at 100 mAh and the CR2025 at 170 mAh, each to 2.0 V, with self-discharge of about 1 percent a year. A 3 V coin and a 1.55 V button are never interchangeable in either direction.

Light-powered watches use none of these

A Citizen Eco-Drive or a Seiko Solar stores its energy in a rechargeable secondary cell. Citizen names it a manganese dioxide lithium cell, as our Eco-Drive movement page sets out; it is a service part, and nothing in the table above replaces it. A stopped light-powered watch needs light first and the service center second, as our comparison of Eco-Drive and Seiko Solar explains. Kinetic and other rotor-charged quartz watches also use a rechargeable cell, covered in do automatic watches need a battery, and a mechanical watch needs no cell at all, one of the differences weighed in quartz versus automatic and in our longer quartz versus mechanical guide.

When this answer stops applying

• The watch maker names a cell. A manual that says 376 or SR626W overrides the general advice to prefer SW. Our guide to reading a watch specification shows where to look.
• The watch is light or motion powered. Nothing on this page applies to its rechargeable cell.
• The cell is old stock. Silver oxide loses capacity on the shelf, faster when warm: under 5 percent a year at 20 °C for Renata's 377, about 2 percent for Maxell's SR626SW.
• The watch still will not run. If a correct, fresh cell does not start it, the fault is the contacts, the coil or the lubrication, and a stopped quartz watch walks through them.

After the cell goes in

A fresh cell brings a quartz watch straight back to its rated accuracy. If the watch is water resistant, have the gasket checked and the watch pressure tested once the back has been off; the service cost guide has typical figures. And take the cell out of a watch you will not wear for a long time, since a flat cell can leak onto the movement, as our guide to servicing and care explains.