Index / 1177SO

1177SO

1177SO — silver oxide, 1.55 V, 11.6 x 1.6 mm. Not listed by Energizer. The closest it still lists: SR44 is too tall to close, and runs the same 1.55 V.

Warning — button cell

1177SO is a button cell: 11.6 mm across and 1.6 mm tall. United States law defines that class by the shape alone — a single cell battery with a diameter greater than its height, 16 CFR 1263.2 — and not by what is inside it. Swallowed, a cell this shape can lodge instead of passing, and it is the current, not the metal, that does the damage. If one has been swallowed, or put in a nose or an ear, call the United States national Poison Help line at 1-800-222-1222 straight away and do not wait for symptoms.

At 11.6 mm and 1.55 V it is under the 16 mm diameter that lodges most readily — which makes it easier to swallow, not safer. The same current runs for as long as it sits.
Reese's Law (15 U.S.C. 2056e) and 16 CFR part 1263 put child-resistant packaging and a warning label on this class; packages manufactured or imported after 21 September 2024 carry it. That is why the pack is hard to open.
The same rule says what to do with the used cell, in its own words: dispose of it at once, keep it away from children, and do NOT put it in household trash (16 CFR 1263.4(b)(3)). Tape over both faces first — a cell too flat to run a watch still has enough left to burn.

What fits the compartment, and what does not

Fit answers whether it enters the compartment. Voltage answers whether the circuit will notice. A cell that fits is not always a safe substitute.

Cell	Fit	Voltage	Chemistry	Capacity
SR44	too tall	1.55 V 0%same volts	silver oxide	195 mAh
SR43	too tall	1.55 V 0%same volts	silver oxide	110 mAh
SR42	too tall	1.55 V 0%same volts	silver oxide	100 mAh
SR54	too tall	1.55 V 0%same volts	silver oxide	85 mAh
SR55	too tall	1.55 V 0%same volts	silver oxide	55 mAh
LR44	too tall	1.5 V -3.2%close enough	alkaline	150 mAh
LR43	too tall	1.5 V -3.2%close enough	alkaline	113 mAh
LR54	too tall	1.5 V -3.2%close enough	alkaline	66 mAh
PR44	too tall	1.45 V -6.5%reads off	zinc air	—
CR11108	too tall	3 V +93.5%wrong class	lithium	160 mAh

Nothing Energizer still lists is the same depth. The 10 options below share the diameter and run 2 to 10.8 mm against this cell's 1.6, and every one of them is deeper than this cell, so the question is not the contact but the cover: a deeper cell goes into the opening and stops the lid closing.

Also stamped 366

Nominal1.55V

Diameter11.6mm

Height1.6mm

Capacity33mAh

In the Energizer catalogNot listed

Unlisted, and everything listed is deeper

Energizer no longer lists 1177SO (also 366), and everything listed at this diameter is deeper: SR44 stands 5.4 mm where this one stands 1.6. It will go into the opening and it will not let the cover close, so there is nothing here to shim or pack out.

What the chemistry changes

Everything above answers size and voltage. What it cannot answer is chemistry, and 1 other kind is in play here beside the silver oxide this cell uses.

Silver oxide holds its voltage almost flat until it is spent, which is why watches and light meters were built around it.
Alkaline drops in voltage steadily as it empties, so a device calibrated for a flat discharge will drift as it goes.

From BatteryCrossEvery designation in one pageEach code with what it measures and what it replaces

What a watch movement does with this cell

A quartz movement pulls a short pulse through the cell every second and reads the voltage between pulses. That is why the chemistry in this envelope matters more than the size does. Silver oxide holds 1.55 V nearly flat until it is spent.

Internal impedance 20 to 30 ohms, published by the maker. That is the figure the stepper motor pulse sees, and it rises as the cell ages. Energizer no longer lists 1177SO, so the cell in the case of an older watch may have no current part under this designation at all. 10 cells measure close enough to compare against it in the Energizer data this site reads, and 10 of them are still listed.

The nearest is SR44: it goes in and stands too tall and runs 1.55 V, same volts.
By stored energy it stands 1 of 2 in its envelope, at 51 milliwatt-hours.
Energizer files it for North America, which is where the part is sold rather than where the cell will work.
Energizer no longer lists 1177SO at all, so whatever goes into that compartment next will be a substitution rather than a replacement.

Drawn to scale

1177SO, side elevation, from the published figures

The same scale for all of them. The dashed line marks the height of 1177SO: a silhouette that stops short of it will not reach the contact, one that crosses it will not let the cover close.

This cellAnother cell, same scale

Every published figure

Every field the maker fills is filled for this one: 12 figures in all, from chemistry through to where it is sold.

Designation	1177SO
Also stamped	366
Chemistry	Silver Oxide
Nominal voltage	1.55 V
Diameter	11.6 mm
Height	1.6 mm
Weight	0.6 g
Volume	0.17 cc
Capacity	33 mAh to 1.2 V
Stored energy	51 mWh
Energy density	301 mWh per cc
Impedance	20 to 30 ohms
In the Energizer catalog	No longer listed
Listed for	North America

2 rows in the table are not the maker's but ours: stored energy and energy per cubic centimeter. Everything else is reproduced without change.

The number a pulse sees

Energizer publishes an impedance band of 20 to 30 ohms for 1177SO. It is the least quoted number on the sheet and the one that decides whether the cell can drive a pulse; 3 other published figures sit below.

The part occupies 0.17 cubic centimeters and weighs 0.6 g. Capacity and voltage together put 51 milliwatt-hours in that space. Energizer files it for North America.

Internal impedance: 20 to 30 ohms as published. A high-impedance cell sags under a pulse and recovers between pulses, which is what a movement or a sensor sees.
Cutoff voltage: 1.2 V. The published capacity is counted down to this voltage; a device that quits higher up sees less than the whole figure.
Mass against volume: 0.6 g filling 0.17 cubic centimeters. When the printing has worn off, a kitchen scale separates two cells of one envelope faster than a caliper does.
Where the part is filed: North America. That is a statement about the maker's distribution and not about where the cell works.

Is that a lot of energy?

Nothing else measured in this shell holds more. At 51 milliwatt-hours it leads 1 other cell, and the next one down carries 91% of what it does. Per unit of volume that is 301 mWh per cubic centimeter, denser than 39% of everything measured here.

A width the catalog keeps returning to

11.6 mm is a width this catalog keeps coming back to: 20 coins sit within half a millimeter of it, 1177SO included.

10 of those ones are still listed. Its 301 milliwatt-hours per cubic centimeter sit above 39 percent of everything here that publishes both a capacity and a volume. 32 of the 82 coins share its 1.55 V exactly.

SR69 — the next step down by volume: 0.15 cubic centimeters against this cell's 0.17.
SR41 — the next step up: 0.18 cubic centimeters, 106% of this one.
CR11108 — 11.6 x 10.8 mm, 3 V, lithium.
LR43 — 11.6 x 4.2 mm, 1.5 V, alkaline.

The maker's own part numbers

1177SO carries 1 name beyond the designation, and every one of them is a manufacturer part number: a catalog line, not a size and not a standard.

366 — a manufacturer part number for 1177SO, not a standard designation.

The cell that differs only in depth

The code says the size, so the cells that get confused with 1177SO are the ones that keep its diameter and change its depth. 19 cells share this diameter at depths from 2 to 10.8 mm, and every one of them enters the same opening.

It stands 1 of 2 in this envelope by stored energy. On a scale the difference shows before it shows on a caliper: this one weighs 0.6 g.

SR55 — same diameter, 2 mm tall against this cell's 1.6: 0.4 mm deeper, which neither designation carries.
LR55 — same diameter, 2.1 mm tall against this cell's 1.6: 0.5 mm deeper, which neither designation carries.
LR54 — same diameter, 3.1 mm tall against this cell's 1.6: 1.5 mm deeper, which neither designation carries.
BR1225 — 12.5 mm across at 3 V against 11.6 mm here, 0.9 mm apart: too wide to enter in this holder.
CR1216 — 12.5 mm across at 3 V against 11.6 mm here, 0.9 mm apart: too wide to enter in this holder.

One figure the maker does not publish

One field is empty for 1177SO: operating temperature. A blank means the maker publishes no figure, which is not the same as zero, and it is the reason one comparison below is missing rather than wrong.

The blanks are the same in all 1 record behind this designation, so they are the catalog's silence and not a merge losing a value. What is not missing is the envelope: 11.6 x 1.6 mm, published and checked against the designation itself.

No operating temperature — so this page cannot tell you whether the maker claims anything at all below freezing.

Before you swap anything

Everything here is computed from published dimensions and nominal voltages. That answers whether a cell enters the compartment and whether the voltage matches on paper. It does not answer what your device does with the difference, and it cannot: a cell that fits can still be the wrong cell.

One more limit, and it is the biggest. This site reads a single manufacturer’s catalog. When a page says a designation is not listed, that means Energizer no longer offers a part under it — not that nobody makes the cell. Other makers may still sell it, and for common sizes they usually do.

A voltage difference is one relation between two cells, and this page prints it from the cell it is about — in every table on the page, including the one listing cells no longer made. A figure always belongs to the cell whose voltage is printed beside it: a cell that runs lower than this one carries a minus here, one that runs higher carries a plus, and two cells at the same nominal voltage carry zero. Meet the same pair on the other cell’s page and the sign is the other one, with the figure taken against that cell instead of this one; where the two run at the same voltage, both pages print zero. The class beside the figure is not read off that figure directly. It is decided on the gap itself, taken against the higher of the two nominal voltages, so one pair of cells gets one class whichever page you meet it on: counted from this side the boundary of the class that still runs falls at 20.0% below and 25.0% above, which is the same gap divided once by the larger nominal and once by the smaller. What genuinely differs between the two directions is the consequence, and the words carry it: a cell that runs low makes a calibrated instrument read below true, and a cell that runs high makes it read above.

3 things this site cannot see. Whether the contacts reach a shorter cell. Whether the device was calibrated for a chemistry that holds its voltage flat, which silver oxide does and alkaline does not. Whether the equipment tolerates the higher current a different chemistry can deliver. Rechargeable cells are never a drop-in for primary cells regardless of size.

Cells measured next to this one

1 cell sits at exactly this size, and 19 more share the diameter at other depths. The first group is interchangeable by measurement; the second is not.

365 — 11.6 x 1.6 mm, 1.55 V
SR55 — 11.6 x 2 mm, 1.55 V
LR55 — 11.6 x 2.1 mm, 1.5 V
LR54 — 11.6 x 3.1 mm, 1.5 V
SR54 — 11.6 x 3.1 mm, 1.55 V

Where these numbers come from

Dimensions, voltages, chemistries and capacities are published by the manufacturer and reproduced without change. Everything else on the page is ours, computed from those figures: whether one cell fits where another sat, how far apart their voltages are, stored energy and energy per cubic centimeter, the rank within a shell, and the check of the designation against the measured size.

Fit is decided within 0.3 mm on every axis, which is the order of a contact spring's travel. Voltage classes are decided by consequence, not by roundness, and they are decided on the gap between two nominal voltages taken against the higher of the two: 2.0% or less of it is the same working voltage, 6.0% starts to matter to a calibrated instrument, and past 20.0% it is a different class altogether. Measuring the gap against the higher figure is what makes the verdict the same from either cell’s page, while the printed percentage stays counted from the cell you are reading about. Cells with identical stored energy share a rank instead of being ordered arbitrarily.

Ranking uses capacity times nominal voltage, because capacity alone is not comparable across chemistries: 150 mAh at 3 V is twice the energy of 150 mAh at 1.5 V. Neighbors are chosen by measurement and never alphabetically, because two cells filed next to each other by name usually have nothing in common. A blank in any table means the maker publishes no figure, which is not the same as zero.

Source: Energizer technical data, retrieved 1 September 2026.

The record behind this page

Every figure on this page comes from one catalog record, number 522, and it is linked below. The sheet is the document the dimensions, voltage and capacity were read out of.

[1] Energizer catalog record 522, listed as 366, obsolete in the snapshot. Technical data sheet: 366.pdf.

Every figure above is reproduced from those records without change; the comparisons are ours and are described on the method page. Snapshot: Energizer technical data, retrieved 1 September 2026.

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