Battery type SR44 — compatible cameras

The SR44 is a silver oxide button cell (zinc/silver oxide chemistry) with a nominal voltage of 1.55 V and dimensions of 11.6 × 5.4 mm. It has been a worldwide standard button cell since the 1970s and is produced by manufacturers like Varta, Renata, Maxell, Sony, and Energizer. Common synonyms are 357, 303, S76, MS76, SR44W, and SR44SW. Compared to alkaline cells, silver oxide delivers a significantly more constant voltage over the entire discharge curve — the reason it has become standard for analog light meters.

SR44 is typically used in pairs (2x SR44 = 3.1 V) in a limited group of analog cameras: Leica R3 and R3 MOT, Minolta CLE, and Honeywell Pentax Auto 110. The complete searchable list with all models and manuals can be found at the top of this page. Beyond this camera group, the SR44 is also the standard button cell for many handheld light meters, small flash units, and last but not least as a power source for Schottky diode adapters that regulate it down to 1.35 V.

The two cells are identical in size (11.6 × 5.4 mm) and fit mechanically in the same battery compartments — but their chemistry is different, which makes a practical difference in analog cameras:

• SR44 (Silver Oxide): 1.55 V nominal voltage, which remains nearly constant over about 90% of the discharge curve. Typical lifespan in a light meter is one to two years.
• LR44 (Alkaline): 1.5 V fresh, but continuously drops to about 1.0 V. Cheaper to buy, but delivers fluctuating readings over its lifetime — a worse choice for a light meter.

If your camera manual calls for SR44, you should use SR44 and not replace it with LR44. The small price difference is easily made up for by the much more accurate light metering.

Not directly. The SR44 has 1.55 V, the historic PX625 mercury cell had 1.35 V — a difference of 0.2 V that leads to about one to 1.5 stops of underexposure in many cameras (higher voltage makes the light meter assume more light → it closes the aperture). Also, the SR44 is mechanically smaller (11.6 × 5.4 mm vs. 16 × 11.2 mm).

There are two clean ways to still use an SR44 in a PX625 camera: First, a PX625 adapter with Schottky diode that regulates the voltage down and compensates mechanically — however, battery check does not work reliably here. Second, if your camera has a so-called bridge circuit (e.g., Pentax Spotmatic), the camera electronics compensate for the voltage difference automatically — then the pure mechanical adapter without diode is sufficient.

A light meter does not measure light directly but interprets the voltage at its input terminals as a measure of light intensity. If this voltage changes over the battery's lifetime, the measured value changes too — even if the actual light remains the same. Too high a voltage (alkaline 1.5 V instead of the expected 1.35 V) leads to underexposure because the camera assumes more light than is really there and closes the aperture; too low a voltage causes overexposure. Negative film forgives overexposure much better than underexposure — so a slight undervoltage is generally the lesser evil.

Even more important than the absolute value is the consistency: Alkaline cells like the LR44 continuously drop their voltage from 1.5 V to around 1.0 V and deliver fluctuating readings over their lifetime. Silver oxide (SR44), on the other hand, keeps its 1.55 V almost stable over about 90% of the discharge — which is why it was the natural successor to the mercury cell in the 1970s for all cameras factory-designed for 1.5 V. Zinc-air and NiMH cells behave similarly consistently and are the cleaner options for the historic 1.35 V cameras.