Battery type PX675 — Compatible Cameras

The PX675 (IEC designation MR44, other names EPX675, RM675, H-C, V675PX) is a 1.35-volt mercury cell based on zinc-mercury oxide (Zn/HgO), produced from the 1960s by Mallory, Varta, and Duracell for light meters in analog cameras. Measuring 11.6 × 5.4 mm, it is significantly smaller than the related PX625 (15.6 × 5.95 mm) and was used in especially compact camera bodies. Like all mercury cells, its voltage remains extremely stable throughout discharge — a property essential for the correct function of analog light meters.

The PX675 was used in numerous compact rangefinder and SLR cameras from the 1960s to 1970s: Konica C35 and C35 family (Automatic, EF, FD, Flashmatic), Konica Auto S3, the entire Konica Autoreflex T series, Olympus Pen D3, Minolta Hi-Matic G and G2, Petri Color 35 and Petri FT series, Chinon 35 series, Cosina 35 and Hi-Lite series, Ricoh 500 series, Vivitar 220/SL to 420/SL, Miranda Sensomat and Sensorex II. You can find the full searchable compatibility list at the top of this page.

Mercury-containing button cells like the PX675 have been gradually banned in the EU. The original Battery Directive 2006/66/EC initially still included an exemption for button cells (up to 2 wt% mercury allowed). Only the amendment directive 2013/56/EU closed this loophole — effective from October 1, 2015, button cells may no longer contain relevant amounts of mercury. In Germany and the UK, the import of PX675 was effectively illegal since September 18, 1992, under the predecessor directive 91/157/EEC. In the USA, a comparable ban has been in place since 1996 under the Mercury-Containing and Rechargeable Battery Management Act. The reason is not the battery itself, but the environmental pollution caused by mercury in improper disposal.

The PX675 has a technical peculiarity that makes replacement significantly easier than with the larger PX625: modern zinc-air hearing aid batteries type 675 (IEC designation PR44) have exactly the same form factor as the old PX675 (11.6 × 5.4 mm) and are therefore a direct, mechanically fitting replacement — in most cameras without any adapter. Still, each option has its own pros and cons:

• Zinc-air hearing aid batteries type 675 (direct replacement): The cheapest and simplest solution for most PX675 cameras — fits directly into the battery compartment, delivers 1.4 V (close enough to the mercury reference value of 1.35 V) with a flat discharge curve. Disadvantage: after activation (removal of protective foil), the cell lasts only about three to six weeks because it continuously consumes oxygen from the air. Available at Ausgeknipst as a zinc-air refill pack type 675.
• Wein-Cell MRB675: Zinc-air cell specially made for PX675 cameras with reduced air supply, resulting in a longer lifespan than standard hearing aid batteries. Relatively expensive and only available in specialty photo stores.
• Rechargeable battery (Varta V80H) with charger: NiMH cell with a nominal voltage of 1.2 V — about 0.15 V below the mercury reference value of 1.35 V, leading to a slight systematic overexposure of around half a stop (not critical for color negative film, but noticeable for slide film). The advantage is the flat discharge curve and reusability. Note: V80H primarily corresponds to PX625 in form factor; a simple spacer ring or adapter may be needed for PX675 compartments. Available at Ausgeknipst as a USB-C charging set with V80H.
• Adapter with Schottky diode for SR44: Regulates a normal silver oxide SR44 down to 1.35 V. Advantage: standard batteries available everywhere, long shelf life. Disadvantage: camera battery check often does not work correctly, and the adapters are expensive. Currently mainly offered by Kanto Kamera (Japan) — an Ausgeknipst version is in development.

It depends on the camera, film, and chosen replacement battery. Higher voltage than 1.35 V (alkaline 1.5 V, silver oxide 1.55 V) causes the light meter to accept too much light → the camera closes the aperture or shortens the exposure time → about one to 1.5 stops underexposure. Lower voltage leads to overexposure. With slide film, any misexposure is critical; color negative film forgives one to two stops and reacts much more forgivingly to overexposure than underexposure — slight undervoltage is therefore generally the lesser evil.

Even more important than the absolute voltage value is the consistency over the entire discharge curve. Alkaline cells (LR44, V625PX) continuously lose voltage and deliver fluctuating readings over their lifetime — they are especially unsuitable for analog light meters. Mercury cells like the PX675, on the other hand, kept their voltage constant at 1.35 V over about 95% of the discharge — exactly why they were historically successful. Zinc-air (675 hearing aid batteries, Wein-Cell) hits the mercury target voltage very accurately at 1.4 V and also has a flat discharge curve. NiMH (Varta V80H) also has the same flat discharge curve but is about 0.15 V below the target at 1.2 V — therefore, the V80H battery leads to slight overexposure (~½ stop), which is not critical for color negative film. Silver oxide cells (SR44) are also voltage stable but are too high at 1.55 V and therefore require the diode adapter.