PX27 Battery: Compatible Cameras

The PX27 is a 5.6-volt mercury battery (nominal voltage; 5.4 V under load) made up of four stacked NR43 mercury cells. Dimensions: approx. 13 mm in diameter × 20.5 mm high. From the 1970s onwards it was made by Mallory, Varta and Duracell for compact camera bodies that simply had no room for the wider PX625. Common cross-reference designations: V27PX, 4NR43, H-4D, TR-164.

The PX27 was used mainly in the Minox 35 family of the late 1970s and the 1980s: the Minox 35 EL, GL, GT, PL, PE and AL, as well as the Minox subminiature cameras C, CLX, EC, ECX, LX and TLX, the Minox light meter and the FL4 flash. The later Minox 35 models from 1988 onwards (GT-E, GT-E II, GS-E, GT-S, GT-X and the gold-button edition), on the other hand, don’t take a PX27 but 2x CR 1/3N in the built-in battery holder. Several Rollei compacts also use the PX27: the Rollei 35 LED, 35SE, 35TE, A110 and E110. The Agfa Optima 335 and Optima Sensor Flash and the Hanimex VEF Zoom are on the list too. You’ll find the complete searchable list at the top of this page.

Like all mercury button cells, the PX27 was banned in the EU under Battery Directive 2006/66/EC (and its amendment 2013/56/EU). The last remaining stocks ran out somewhere between about 2009 and 2015. The reason isn’t the battery itself but the environmental damage mercury causes when it isn’t disposed of properly. Compared with the PX625, this makes the PX27 doubly hard to replace: not only is old stock even rarer, its construction is also unusual (4 stacked cells instead of a single button cell).

There’s no single “best” replacement; each option has its own strengths and weaknesses:

• Four stacked SR44s (silver oxide) with an adapter sleeve: 6.2 V in total. Standard button cells you can get anywhere, long life, and constant voltage across the entire discharge curve. Available from Ausgeknipst as the Minox 35 battery with adapter. The sleeve holds the four SR44s in the right position in the battery compartment and ensures proper electrical contact.
• Four stacked LR44s (alkaline) in the same sleeve: Also around 6 V and much cheaper than SR44s, but alkaline cells lose voltage steadily, which skews the meter readings over their lifetime. Not recommended for serious slide film work.
• Exell S27PX (silver oxide) or Golden Power PX27A (alkaline): Both are direct-replacement cells in the PX27 format that are still in production, 6 V, and go in without an adapter. Pro: plug-and-play. Con: only available from specialist photo retailers, expensive at around €15 to €20 per cell, and lower in capacity than the 4-cell solution. The silver oxide version (Exell) holds its voltage more steadily across the discharge curve, so it’s the better choice for slide film; the alkaline version (Golden Power) is cheaper but electrically less stable.
• Type 675 hearing aid batteries with an adapter (zinc-air): The closest match to the original in terms of voltage (1.4 V per cell, four of them ≈ 5.6 V), available from Ausgeknipst as a zinc-air refill pack. We don’t currently stock a ready-made adapter set for the PX27; an Ausgeknipst version with a Schottky diode for full metering accuracy is in development.

Yes, but usually less dramatically than people fear. The classic Minox 35 models (EL, GL, GT, PL) have a bridge circuit in the light meter, which makes them fairly tolerant of voltage differences, and electrically the 6.2 V solution with four SR44s is no problem. In practice, though, these models can underexpose slightly, by around ½ to 1.5 EV, because the meter assumes “more light” at the higher voltage. To compensate, set the ISO dial half a stop to a full stop lower (for example, ISO 200 film at ISO 100 or 125).

What matters more than the absolute voltage, however, is how constant it stays across the discharge curve: alkaline cells (LR44) lose voltage steadily and give drifting readings over their lifetime. Silver oxide (SR44), zinc-air (type 675) and mercury, by contrast, hold their voltage steady for most of the discharge, and that’s exactly what makes them the technically cleaner replacement options. So for slide film, which shows up every exposure error, SR44s or the zinc-air option are worth it; colour negative film easily forgives one to two stops of over- or underexposure.