Index / MR50

MR50

MR50 — mercuric oxide, 1.4 V, 16 x 16.5 mm. Not listed by Energizer, and nothing in its catalog shares this size.

Also stamped 1100MP, EPX1

A mercury cell, and why nothing is a straight swap

This is a mercuric oxide cell, and mercury cells are banned from consumer sale in the United States and the European Union: the chemistry was outlawed, not merely retired. Nothing Energizer still lists holds 1.4 V the way it did, and the 16 x 16.5 mm shell has 0 neighbors of other depths but no equal.

The instruments this cell was calibrated into

Mercuric oxide was chosen for one property: it held its voltage almost flat until it died, so a light meter or an exposure circuit could be calibrated against it and stay calibrated. MR50 is a 1.4 V cell, and the chemistry is banned for consumer sale in the United States and the European Union.

Zinc air comes closest in voltage and is still made: PR41, PR43 and PR44 run 1.45 V. It is a different envelope and a different discharge life, and it is the direction the photographic trade took. A cell that reads off does not announce itself. The needle moves, the numbers look plausible, and the exposure is wrong by a fixed amount every time.

• Energizer files it for North America, which is where the part is sold rather than where the cell will work.
• Energizer no longer lists MR50 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 EPX1.

Older equipment, manuals and repair notes call it PX1 — the same designation without the maker’s letter in front.

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.

What the datasheet does not say

Beyond size and voltage the sheet for MR50 is thin: 2 published figures below, and no impedance, no cutoff and no operating range at all. That silence is the maker's, not ours.

The part occupies 3.3 cubic centimeters and weighs 14.3 g. Capacity and voltage together put 1400 milliwatt-hours in that space. Energizer files it for North America.

Mass against volume

14.3 g filling 3.3 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: 1400 milliwatt-hours in 3.3 cubic centimeters is 424 mWh per cc, denser than 69% 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

16 mm is a width this catalog keeps coming back to: 3 cylinders sit within half a millimeter of it, MR50 included.

2 of those ones are still listed. Its 424 milliwatt-hours per cubic centimeter sit above 69 percent of everything here that publishes both a capacity and a volume. 1 of the 69 cylinders shares its 1.4 V exactly.

• LR50 — the next step down by volume: 3.2 cubic centimeters against this cell's 3.3.
• 4NR43 — the next step up: 3.4 cubic centimeters, 103% of this one.
• CR15H270 — 15.6 x 27 mm, 3 V, lithium.
• CR2 — 15.6 x 27 mm, 3 V, lithium.

The mercury-era part numbers

Before the chemistry changed, this envelope was sold under part numbers rather than a designation. 1 number of them still turn up on old equipment and in old manuals, alongside 2 current names.

• PX1 — a mercury-era part number for this envelope, carried over by the trade after the chemistry left it.
• 1100MP — a manufacturer part number for MR50, not a standard designation.
• EPX1 — a manufacturer part number for MR50, not a standard designation.

Near the same width, and not the same cell

No other cell in the Energizer data this site reads measures this exactly, so the confusions are the near misses: 13 cells sit within a millimeter of this cell's 16 mm and do not fit its holder.

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 14.3 g.

• CR15H270 — 15.6 mm across at 3 V against 16 mm here, 0.4 mm apart: loose in this holder.
• CR2 — 15.6 mm across at 3 V against 16 mm here, 0.4 mm apart: loose in this holder.

What this page cannot tell you

3 of the 7 fields this site reads are empty for MR50: cutoff voltage, 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: 16 x 16.5 mm, published and checked against the designation itself.

• No cutoff voltage — so this page cannot tell you what the capacity figure was counted down to, without which the capacity is a number without a scale.
• 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.

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 838, and it is linked below. The sheet is the document the dimensions, voltage and capacity were read out of.

1. [1] Energizer catalog record 838, listed as EPX1, obsolete in the snapshot. Technical data sheet: epx1.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/mr50/. It loads nothing from anywhere else. Paste this:

<iframe src="https://batterycross.com/embed/mr50/" width="100%" height="520" loading="lazy" title="MR50 replacements"></iframe>