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 mercury cells of type NR43. Dimensions: about 13 mm diameter × 20.5 mm height. It was manufactured from the 1970s by Mallory, Varta, and Duracell for compact camera bodies where there simply was no room for a wider PX625. Common cross-reference designations: V27PX, 4NR43, H-4D, TR-164.

The PX27 was mainly used in the Minox 35 family from the late 70s and 80s: Minox 35 EL, GL, GT, GTE, GTX, PL, PE, AL, GSE, C, CLX, EC, ECX, LX, TLX as well as Minox light meter and flash FL4. In addition, several Rollei compact models 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 by Battery Directive 2006/66/EC (and its amendment 2013/56/EU) — the last remaining stocks were used up roughly between 2009 and 2015. The reason is not the battery itself, but the environmental impact of mercury in improper disposal. Unlike the PX625, the PX27 is doubly difficult to replace: it is not only rarer in remaining stock but also structurally unusual (4 stacked cells instead of a single button cell).

There is no single "best" replacement — each option has its own strengths and weaknesses:

• Four stacked SR44 (Silver Oxide) with adapter sleeve: Total voltage 6.2 V. Standard button cells available everywhere, long shelf life, constant voltage over the entire discharge curve. Available from Ausgeknipst as Minox-35 battery with adapter — the sleeve correctly positions four SR44 cells in the battery compartment and ensures electrical contact.
• Four stacked LR44 (Alkaline) with the same sleeve: Voltage also around 6 V, significantly cheaper than SR44 — but alkaline continuously drops voltage and thus distorts exposure metering over its lifetime. 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, usable without an adapter. Advantage: Plug-and-play. Disadvantage: Only available through specialty photo stores, expensive at around 15 to 20 € per cell, and with lower capacity than the 4-cell solution. The silver oxide variant (Exell) maintains voltage more consistently over the discharge curve and is therefore preferable for slide film; the alkaline variant (Golden Power) is cheaper but electrically less stable.
• Hearing aid batteries Type 675 with adapter (zinc-air): Voltage-wise closest to the original (1.4 V per cell, four of them ≈ 5.6 V), available at Ausgeknipst as a zinc-air refill pack. Currently not available as a ready adapter set for the PX27 — an Ausgeknipst version with Schottky diode for full exposure accuracy is in development.

Yes, but usually less dramatic than often feared. The Minox-35 classics (EL, GL, GT, PL) have a bridge circuit in the light meter and are therefore relatively voltage tolerant — electrically, the 6.2 V solution with four SR44s is uncritical. In practice, however, these models can experience slight underexposure of about ½ to 1.5 EV because the light meter assumes "more light" at higher voltage. You can counteract this by setting the ISO dial half to one full stop lower (e.g., ISO 200 film at ISO 100 or 125).

More important than the absolute voltage value is the consistency over the discharge curve: Alkaline cells (LR44) continuously lose their voltage and provide drifting measurements over their lifetime. Silver oxide (SR44), zinc-air (Type 675), and mercury, on the other hand, keep the voltage constant over most of the discharge — which is exactly what makes them the technically cleaner replacement options. For slide film, which shows every exposure error clearly, SR44 or the zinc-air variant is worthwhile; for color negative film, one or two stops of over- or underexposure are easily forgiven.