Battery type PX27: Compatible cameras

The PX27 is a 5.6-volt mercury battery (nominal voltage; 5.4 V under load) consisting of four stacked NR43-type mercury cells. Dimensions: approximately 13 mm in diameter × 20.5 mm in height. From the 1970s onward, it was manufactured by Mallory, Varta, and Duracell for compact camera bodies where there simply was not enough room for a larger 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 1980s: Minox 35 EL, GL, GT, PL, PE, and AL, as well as in the Minox subminiature cameras C, CLX, EC, ECX, LX, and TLX, plus the Minox light meter and FL4 flash. The later Minox 35 models from 1988 onward (GT-E, GT-E II, GS-E, GT-S, GT-X, and the Gold Button Edition), on the other hand, do not require a PX27, but use 2x CR 1/3N batteries in the built-in battery holder. Several Rollei compact models also use the PX27: Rollei 35 LED, 35SE, 35TE, A110, and E110. The Agfa Optima 335 and Optima Sensor Flash, as well as the Hanimex VEF Zoom, are also included. You can find the complete searchable list at the top of this page.

Like all mercury button cells, the PX27 was banned in the EU under the Batteries Directive 2006/66/EC (and its amendment 2013/56/EU). The remaining stocks were exhausted approximately between 2009 and 2015. The reason is not the battery itself, but the environmental impact of mercury when improperly disposed of. Unlike the PX625, the PX27 is therefore even more difficult to replace: it is not only rarer in remaining stocks, but also structurally unusual, consisting of four stacked cells rather than a single button cell.

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

• Four stacked SR44 (silver oxide) cells with an adapter sleeve: Total voltage 6.2 V. Standard button cells are available everywhere, offer long shelf life, and maintain a constant voltage throughout the discharge curve. Available from Ausgeknipst as a Minox 35 battery with adapter. The sleeve positions four SR44 cells correctly in the battery compartment and ensures electrical contact.
• Four stacked LR44 (alkaline) cells with the same sleeve: The voltage is also around 6 V, significantly cheaper than SR44 cells, but alkaline voltage drops continuously, distorting exposure metering over the cells' service life. Not recommended for serious slide-film photography.
• Exell S27PX (silver oxide) or Golden Power PX27A (alkaline): Both are still-produced direct replacement cells in the PX27 format, 6 V, and can be used without an adapter. Advantage: Plug-and-play. Disadvantage: Available only through specialist photo retailers, expensive at around €15 to €20 per cell, and with lower capacity than the four-cell solution. The silver oxide version (Exell) maintains a more constant voltage throughout the discharge curve and is therefore preferable for slide film; the alkaline version (Golden Power) is cheaper but electrically less stable.
• Type 675 hearing-aid batteries with adapter (zinc-air): Technically closest to the original (1.4 V per cell, four of them ≈ 5.6 V), available from Ausgeknipst as a zinc-air refill pack. For the PX27, it is currently not available as a ready-made adapter set in the range; an Ausgeknipst version with a Schottky diode for full exposure accuracy is in development.

Yes, but usually less dramatically than is often feared. The Minox 35 classics (EL, GL, GT, PL) have a bridge circuit in their light meter and are therefore relatively voltage-tolerant; electrically, the 6.2 V solution with four SR44 batteries is unproblematic. In practice, however, these models may produce slight underexposure of around ½ to 1.5 EV because the light meter interprets the higher voltage as "more light." You can compensate by setting the ISO dial half to one stop lower (e.g., set ISO 200 film to ISO 100 or 125).

However, more important than the absolute voltage is its consistency throughout the discharge curve: alkaline cells (LR44) continuously lose voltage and provide drifting readings over their service life. Silver oxide (SR44), zinc-air (type 675), and mercury batteries, by contrast, maintain a constant voltage through most of the discharge, which is precisely what makes them the technically cleaner replacement options. With slide film, where every exposure error is visible, SR44 or the zinc-air option is therefore worthwhile; with color negative film, over- or underexposure by one or two stops is easily tolerated.