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 about 16 mm diameter × 16 mm height — so it is almost cube-shaped and significantly taller than typical camera button cells like the flat PX625. Common equivalent designations are PX1A, A1PX, PC1A, and 1100A. It has been the established alkaline successor to the historic mercury cell PX1 (also MR50, Mallory RM-1), originally built with a constant voltage of 1.35 V, since the 1990s.

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

No — that is a common confusion. Both have the same diameter of about 16 mm but differ drastically in height: PX625 is flat (≈ 6.2 mm), LR50/PX1 is tall (≈ 16 mm). They are not mechanically interchangeable; a PX625 would rattle loosely in an LR50 slot, and an LR50 does not fit at all in a PX625 compartment. The alkaline version of the PX625 is accordingly not called LR50 but LR9 (or PX625A).

Unlike PX625, the LR50 is not affected by a mercury ban but is a regular alkaline cell available on the market — so you have several options, each with its own strengths and weaknesses:

• Original LR50 / PX1A (alkaline, 1.5 V): Mechanically perfect drop-in, available everywhere, inexpensive. Disadvantage: the 1.5 V is above the original 1.35 V design point, and the alkaline voltage curve continuously drops over the lifetime — causing the light meter to drift depending on the charge state.
• Zinc-air adapter (Ausgeknipst, 1.35 V constant): Our PX1/MR50/LR50 adapter takes an inexpensive 675 hearing aid battery and delivers the original 1.35 V with a mercury-like constant discharge curve. Disadvantage: zinc-air cells only last about four to six weeks after activation.
• Ready-made Wein-Cell for LR50/PX1: Wein Products currently only offers MRB625, MRB675, and MRB400 in their catalog — there is currently no direct Wein-Cell replacement in LR50/PX1 format. Those looking for a ready-made 1.35 V zinc-air cell without an adapter must rely on historical leftover stock or choose the adapter solution.
• NiMH battery Varta V150H / V100H with charger: Rechargeable battery in PX1/LR50 format with cutoff voltage around 1.3 V — close enough to the target value for most light meters. Higher initial cost, but no follow-up costs.

It depends on the camera, film, and chosen replacement battery. Higher voltage than 1.35 V (alkaline LR50 with 1.5 V, even up to 1.6 V when fresh) causes the light meter to accept too much light → typically resulting in up 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 — a 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 like the LR50 continuously drop their voltage from ~1.6 V to below 1.2 V and deliver drifting measurements over their lifetime — this made them particularly unsuitable for analog light meters. Mercury cells, on the other hand, kept their voltage constant at 1.35 V over about 95% of the discharge — this was exactly the reason for their historical success. Zinc-air (675 hearing aid batteries in the adapter) and NiMH (Varta V100H/V150H) behave similarly consistently and are therefore the technically cleaner replacement options.