What battery replaces the PX675?

The PX675 (IEC designation MR44, also known as EPX675, RM675, H-C and V675PX) is a 1.35-volt mercury cell based on zinc/mercuric oxide (Zn/HgO). From the 1960s onward, Mallory, Varta and Duracell made it to power the light meters in film cameras. At 11.6 × 5.4 mm it is considerably smaller than its relative, the PX625 (15.6 × 5.95 mm), and it went into particularly compact camera bodies. Like all mercury cells, it holds its voltage extremely steady throughout its entire discharge, a property that analog light meters depend on to read correctly.

The PX675 was fitted to a wide range of compact rangefinders and SLRs from the 1960s and 1970s: the Konica C35 and the C35 family (Automatic, EF, FD, Flashmatic), the Konica Auto S3, the entire Konica Autoreflex T series, the Olympus Pen D3, the Minolta Hi-Matic G and G2, the Petri Color 35 and Petri FT series, the Chinon 35 series, the Cosina 35 and Hi-Lite series, the Ricoh 500 series, the Vivitar 220/SL to 420/SL, and the Miranda Sensomat and Sensorex II. You’ll find the full, searchable compatibility list at the top of this page.

Button cells containing mercury, like the PX675, were banned in the EU in stages. The original Battery Directive 2006/66/EC still included an exemption for button cells (up to 2% mercury by weight allowed). It was only the amending Directive 2013/56/EU that closed this loophole: from 1 October 2015, button cells may no longer contain any significant amount of mercury either. In practice, though, importing the PX675 into Germany and the UK had already been illegal since 18 September 1992 under the predecessor Directive 91/157/EEC. In the US, a comparable ban has been in force since 1996 under the Mercury-Containing and Rechargeable Battery Management Act. The reason isn’t the battery itself but the pollution mercury causes when it isn’t disposed of properly.

The PX675 has one technical quirk that makes replacing it much easier than the larger PX625: modern size 675 zinc-air hearing aid batteries (IEC designation PR44) have exactly the same form factor as the old PX675 (11.6 × 5.4 mm). That makes them a direct replacement that fits mechanically, in most cameras with no adapter at all. Still, every option has its own pros and cons:

• Size 675 zinc-air hearing aid batteries (direct replacement): The cheapest and, in most PX675 cameras, the most straightforward solution. They drop straight into the battery compartment and deliver 1.4 V (close enough to the 1.35 V of a mercury cell) with a flat discharge curve. Downside: once activated (protective tab peeled off), the cell usually lasts only 2 to 3 months in the camera, because it keeps drawing oxygen from the air. Available at Ausgeknipst as a 675 zinc-air refill pack.
• Wein-Cell MRB675: A zinc-air cell made specifically for PX675 cameras, with restricted air intake, so it lasts longer than standard hearing aid batteries. Relatively expensive and only sold by specialist camera shops.
• Rechargeable battery (Varta V80H): does not fit PX675 cameras. The V80H is the size of the larger PX625 (15.5 mm diameter), while the battery compartment of a PX675 camera is built for 11.6 mm. That’s why our charging kit with the V80H is intended only for cameras with a PX625 compartment. If you’re not sure which compartment your camera has, measure the old cell or the compartment: about 12 mm across means PX675, about 16 mm means PX625. For PX625 cameras, see our PX625 page.
• Adapter with Schottky diode for SR44: Steps a regular SR44 silver oxide cell down to 1.35 V. Pros: standard batteries available everywhere, long life. Cons: the camera’s battery check often doesn’t work properly, and the adapters are expensive. Currently offered mainly by Kanto Kamera (Japan); an Ausgeknipst version is in development.

That depends on the camera, the film and which replacement battery you choose. A voltage higher than 1.35 V (alkaline 1.5 V, silver oxide 1.55 V) makes the light meter think there’s more light than there is → the camera stops down or uses a faster shutter speed → roughly one to 1.5 stops of underexposure. Lower voltage, on the other hand, leads to overexposure. With slide film, any exposure error is critical; color negative film tolerates one to two stops and is far more forgiving of overexposure than underexposure, so a slightly low voltage tends to be the lesser evil.

Even more important than the absolute voltage, though, is consistency across the entire discharge curve. Alkaline cells (LR44, V625PX) lose voltage steadily and give fluctuating readings over their lifespan. That makes them particularly unsuitable for analog light meters. Mercury cells like the PX675, by contrast, held a constant 1.35 V for around 95% of their discharge, and that is exactly why they were so successful back in the day. Zinc-air (675 hearing aid batteries, Wein-Cell) hits the mercury target very closely at 1.4 V and also has a flat discharge curve. Silver oxide cells (SR44) are just as voltage-stable, but at 1.55 V they run too high and therefore need the diode adapter.