Index / 1191SO

1191SO

1191SO — silver oxide, 1.55 V, 5.8 x 2.1 mm. Current, and the only other cells this size are ones Energizer no longer lists: PR63.

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.

Nothing Energizer still lists is the same depth. The 4 options below share the diameter and run 1.2 to 3.6 mm against this cell's 2.1, and some are shallower and some deeper, so read the depth column: short of this cell is a contact problem, past it is a cover problem.

Also stamped 379

Capacity tracks depth almost exactly here

Depth buys capacity here at a steady rate. This cell holds 14.5 mAh in 2.1 mm and 317 holds 11.5 in 1.6 mm, which is the same 6.9 mAh per millimeter of depth: the chemistry fills the shell evenly and the only variable is how much shell there is.

What this cell can stand in for

1 designation Energizer no longer lists points at this cell as the closest thing it does list, and the voltage is not the same: the gap reaches 9.7%. The device will run, and an instrument calibrated for the old cell will read off.

Every column of a row describes the discontinued cell it names. Fit reads that way too: it says whether that cell would enter this compartment, not whether this one enters its. Voltage is measured against this cell, the same way everywhere on the page: each row shows the discontinued cell’s own voltage and how far that voltage sits from this one.

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.
• Zinc air takes oxygen from the air through the holes in its face. It starts discharging the moment the tab comes off and runs down in weeks whether the device is used or not, and a sealed compartment starves it.

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.

PR63 is the same 5.8 x 2.1 mm in zinc air: 1.4 V against this cell's 1.55 V, -9.7%. The case cannot tell them apart; the movement can. Internal impedance 54 to 75 ohms, published by the maker. That is the figure the stepper motor pulse sees, and it rises as the cell ages. 4 cells measure close enough to compare against it in the Energizer data this site reads, and 4 of them are still listed.

• The nearest is 317: it enters and sits lower and runs 1.55 V, same volts.
• By stored energy it stands 2 of 2 in its envelope, at 22 milliwatt-hours.
• Energizer files it for Asia Pacific, Europe, Latin America and North America, which is where the part is sold rather than where the cell will work.
• The maker still lists it, under 1 product line: 379.

Drawn to 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.

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 54 to 75 ohms for 1191SO. 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 0.06 cubic centimeters and weighs 0.2 g. Capacity and voltage together put 22 milliwatt-hours in that space. Energizer files it for Asia Pacific, Europe and Latin America.

Internal impedance

54 to 75 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

0.2 g filling 0.06 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

Asia Pacific, Europe, Latin America and North America. That is a statement about the maker's distribution and not about where the cell works.

Is that a lot of energy?

It holds the least of the 2 cells measured in this shell: 22 milliwatt-hours against 46 for the one directly above. Same compartment, different amount of chemistry inside it. Per unit of volume that is 375 mWh per cubic centimeter, denser than 53% of everything measured here.

A width the catalog keeps returning to

5.8 mm is a width this catalog keeps coming back to: 5 coins sit within half a millimeter of it, 1191SO included.

4 of those ones are still listed. Its 375 milliwatt-hours per cubic centimeter sit above 53 percent of everything here that publishes both a capacity and a volume. 32 of the 82 coins share its 1.55 V exactly.

• 339 — the next step down by volume: 0.053 cubic centimeters against this cell's 0.06.
• 319 — the next step up: 0.07 cubic centimeters, 117% of this one.
• PR63 — 5.8 x 2.1 mm, 1.4 V, zinc air.
• PR70 — 5.8 x 3.6 mm, 1.45 V, zinc air.

The maker's own part numbers

1191SO 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.

• 379 — a manufacturer part number for 1191SO, not a standard designation.

The cell that differs only in depth

The code says the size, so the cells that get confused with 1191SO are the ones that keep its diameter and change its depth. 4 cells share this diameter at depths from 1.2 to 3.6 mm, and every one of them enters the same opening.

It stands 2 of 2 in this envelope by stored energy. On a scale the difference shows before it shows on a caliper: this one weighs 0.2 g.

• 335 — same diameter, 1.2 mm tall against this cell's 2.1: 0.9 mm shallower, which neither designation carries.
• 317 — same diameter, 1.6 mm tall against this cell's 2.1: 0.5 mm shallower, which neither designation carries.
• 319 — same diameter, 2.7 mm tall against this cell's 2.1: 0.6 mm deeper, which neither designation carries.
• PR63 — the same 5.8 x 2.1 mm in zinc air at 1.4 V. Identical on a caliper, different in the circuit.
• 164 — 6.8 mm across at 1.4 V against 5.8 mm here, 1 mm apart: too wide to enter in this holder.

One figure the maker does not publish

One field is empty for 1191SO: 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 2 records behind this designation, so they are the catalog's silence and not a merge losing a value. What is not missing is the envelope: 5.8 x 2.1 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 4 more share the diameter at other depths. The first group is interchangeable by measurement; the second is not.

• PR63 — 5.8 x 2.1 mm, 1.4 V
• 335 — 5.8 x 1.2 mm, 1.55 V
• 317 — 5.8 x 1.6 mm, 1.55 V
• 319 — 5.8 x 2.7 mm, 1.55 V
• PR70 — 5.8 x 3.6 mm, 1.45 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.

Records that disagree behind this page

1191SO is assembled from 2 catalog records, and they do not agree with each other on every field. Both sides are numbered below so the disagreement can be read rather than taken on trust.

1. [1] Energizer catalog record 141, listed as 379, active in the snapshot. Technical data sheet: 379z.pdf.
2. [2] Energizer catalog record 540, listed as 379, obsolete in the snapshot. Technical data sheet: 379.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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