Battery type LR50: Compatible cameras

The LR50 is an alkaline manganese-dioxide button cell with a nominal voltage of 1.5 volts and dimensions of approximately 16 mm in diameter × 16 mm in height. It is therefore nearly cube-shaped and significantly taller than typical camera button cells such as the flat PX625. Common equivalent designations are PX1A, A1PX, PC1A, and 1100A. Since the 1990s, it has been the established alkaline successor to the historical mercury cell PX1 (also known as MR50 or Mallory RM-1), which was originally made with a constant voltage of 1.35 V.

The LR50, or its mercury predecessor PX1, was used in a manageable but highly specific group of cameras from the 1960s and 1970s: Canon Dial 35 (also sold as the Bell & Howell Dial 35 in the United States), Canon Canonet S, Canon Cine Zoom 512, Konica Auto SE, Mamiya 16 Automatic, Minolta Autocord CDS II and CDS III, and Olympus 35 LE. You can find the complete compatibility list at the top of this page.

No. This is a common mix-up. Both have the same diameter of around 16 mm, but differ drastically in height: the PX625 is flat (≈ 6.2 mm), while the LR50/PX1 is tall (≈ 16 mm). They are not mechanically interchangeable; a PX625 would lie loose in the LR50 compartment, while an LR50 will not fit in a PX625 compartment at all. The alkaline version of the PX625 is therefore not called LR50, but LR9 (or PX625A).

Unlike the PX625, the LR50 is not affected by a mercury ban; as an alkaline cell, it is regularly available in stores. So you have several options, each with its own strengths and weaknesses:

• Original LR50 / PX1A (alkaline, 1.5 V): Mechanically perfect drop-in, available to order everywhere, and inexpensive. Disadvantage: The 1.5 V is above the original 1.35 V design point, and the alkaline voltage curve continuously declines over the service life. As a result, the light meter drifts depending on the state of charge.
• Zinc-air adapter (Ausgeknipst, constant 1.35 V): Our PX1/MR50/LR50 adapter takes an inexpensive type 675 hearing-aid battery and delivers the original 1.35 V with a mercury-like constant discharge curve. Disadvantage: Zinc-air cells last only around four to six weeks after activation.
• Ready-made Wein-Cell for LR50/PX1: Wein Products currently lists only MRB625, MRB675, and MRB400 in its catalogue; there is currently no direct Wein-Cell replacement in the LR50/PX1 format. Anyone looking for a ready-made 1.35 V zinc-air cell without an adapter must rely on historical remaining stock or choose the adapter solution.
• NiMH rechargeable battery Varta V150H / V100H with charger: Rechargeable battery in the PX1/LR50 form factor with a charge termination voltage of around 1.3 V, close enough to the target value for most light meters. Higher initial cost, but no ongoing costs.

That depends on the camera, film, and replacement battery selected. A higher voltage than 1.35 V (alkaline LR50 at 1.5 V, and even up to 1.6 V when fresh) makes the light meter assume that there is too much light → typically resulting in underexposure by one to 1.5 stops. Lower voltage conversely leads to overexposure. With slide film, every exposure error is critical; colour-negative film tolerates one or two stops and is noticeably more forgiving of overexposure than underexposure, so a slight undervoltage is generally the lesser evil.

More important than the absolute voltage, however, is its consistency across the entire discharge curve: alkaline cells such as the LR50 continuously drop from ~1.6 V to below 1.2 V and deliver readings that shift throughout their service life. This made them particularly unsuitable for analogue light meters. Mercury cells, by contrast, maintained a constant 1.35 V over around 95% of their discharge, which was precisely the reason for their historical success. Zinc-air cells (675 hearing-aid batteries in an adapter) and NiMH cells (Varta V100H/V150H) behave similarly consistently and are therefore the technically cleaner replacement options.