Index / LR55

LR55

LR55 — alkaline, 1.5 V, 11.6 x 2.1 mm. Not listed by Energizer. The closest it still lists: SR55 drops straight in, and runs 1.55 V — +3.3%, a shade high.

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.

One cell is the same size, and it is not the same voltage: SR55 runs +3.3% against this one, a few hundredths of a volt above, which almost nothing notices. Whether that matters is a question about the device, not about the cell.

Also stamped 191

Unlisted, but something drops straight in

LR55 (also 191) has left the Energizer catalog, but the swap is easy: SR55 is the same 11.6 x 2.1 mm and runs at 1.55 V against this cell's 1.5 V. The same cell is stamped 191 depending on who made it.

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 alkaline this cell uses.

• Alkaline drops in voltage steadily as it empties, so a device calibrated for a flat discharge will drift as it goes.
• Silver oxide holds its voltage almost flat until it is spent, which is why watches and light meters were built around 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. Alkaline at 1.5 V sags as it discharges, and the movement reads that sag as a dying cell.

Published capacity 49 mAh. A movement drawing a few microamps between pulses turns that into years, which is why a watch cell is judged on shelf life. Energizer no longer lists LR55, 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 SR55: it drops straight in and runs 1.55 V, close enough.
• Energizer files it for North America, which is where the part is sold rather than where the cell will work.
• Energizer no longer lists LR55 at all, so whatever goes into that compartment next will be a substitution rather than a replacement.

Drawn to scale

Every published figure

11 figures are published, and one is not: impedance. The row is absent rather than estimated. It reached shelves as 191.

The IEC standard writes this designation in full as LR1120. That form comes from the standard, not from a record of the maker’s, which is why it is not among the markings above.

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.

Where the capacity figure stops counting

A capacity figure means nothing without the voltage it was counted to. For LR55 the maker counts down to 0.9 V, and 2 published figures sit beside it.

The part occupies 0.2 cubic centimeters and weighs 0.8 g. Capacity and voltage together put 74 milliwatt-hours in that space. Energizer files it for North America.

Cutoff voltage

0.9 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

0.8 g filling 0.2 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 shares this shell, so the comparison has to go site-wide: 74 milliwatt-hours in 0.2 cubic centimeters is 368 mWh per cc, denser than 50% of every cell measured here. Density is ours: the maker publishes capacity and volume and never divides one by the other.

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, LR55 included.

10 of those ones are still listed. Its 368 milliwatt-hours per cubic centimeter sit above 50 percent of everything here that publishes both a capacity and a volume. 11 of the 82 coins share its 1.5 V exactly.

• SR57 — the next step down by volume: 0.19 cubic centimeters against this cell's 0.2.
• SR55 — the next step up: 0.22 cubic centimeters, 110% of this one.
• 1177SO — 11.6 x 1.6 mm, 1.55 V, silver oxide.
• CR11108 — 11.6 x 10.8 mm, 3 V, lithium.

The names on the package that are not designations

LR55 answers to 1 marking outside the standard: AG8. A trade marking used by importers, not an iec designation, and no standards body stands behind any of them, which is why none is printed under Also stamped above.

• AG8 — a trade marking used by importers, not an IEC designation.
• LR1120 — the same designation written out in full: the standard's long form for LR55.
• 191 — a manufacturer part number for LR55, not a standard designation.

The cell that differs only in depth

The code says the size, so the cells that get confused with LR55 are the ones that keep its diameter and change its depth. 19 cells share this diameter at depths from 1.6 to 10.8 mm, and every one of them enters the same opening.

It stands 1 of 1 in this envelope by stored energy. On a scale the difference shows before it shows on a caliper: this one weighs 0.8 g.

• 1177SO — same diameter, 1.6 mm tall against this cell's 2.1: 0.5 mm shallower, which neither designation carries.
• 365 — same diameter, 1.6 mm tall against this cell's 2.1: 0.5 mm shallower, which neither designation carries.
• LR54 — same diameter, 3.1 mm tall against this cell's 2.1: 1 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.

What this page cannot tell you

2 of the 7 fields this site reads are empty for LR55: impedance and operating temperature. Everything computed from them is absent from this page rather than estimated.

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 2.1 mm, published and checked against the designation itself.

• No impedance — so this page cannot tell you whether the cell can drive a pulse, which is the whole question in a watch or a sensor.
• 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

Nothing in this data is this exact size, but the diameter is a well populated one: 19 cells run from 1.6 to 10.8 mm deep, and this cell is one point on that scale.

• 1177SO — 11.6 x 1.6 mm, 1.55 V
• 365 — 11.6 x 1.6 mm, 1.55 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 342, and it is linked below. The sheet is the document the dimensions, voltage and capacity were read out of.

1. [1] Energizer catalog record 342, listed as 191, obsolete in the snapshot. Technical data sheet: 191.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.

Putting this on a forum or a repair page? The same answer without the site around it — fit, voltage, chemistry and the limits that go with them — is at /embed/lr55/. It loads nothing from anywhere else. Paste this:

<iframe src="https://batterycross.com/embed/lr55/" width="100%" height="520" loading="lazy" title="LR55 replacements"></iframe>