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 widely used worldwide as a standard button cell since the 1970s and is manufactured by companies such as Varta, Renata, Maxell, Sony, and Energizer. Common synonyms include 357, 303, S76, MS76, SR44W, and SR44SW. Compared with alkaline cells, silver oxide delivers a significantly more constant voltage across the entire discharge curve. That is why it has become established for analogue light meters.

SR44 is typically used in pairs (2x SR44 = 3.1 V) in a limited group of analogue cameras: Leica R3 and R3 MOT, Minolta CLE, and Honeywell Pentax Auto 110. You can find the complete searchable list with all models and instructions at the top of this page. Beyond this group of cameras, 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 differs, which makes a practical difference in analogue cameras:

• SR44 (Silver oxide): 1.55 V nominal voltage, remaining nearly constant over around 90% of the discharge curve. Typical service life in a light meter is one to two years.
• LR44 (Alkaline): 1.5 V when fresh, but it continuously drops to around 1.0 V. Cheaper to buy, but delivers fluctuating readings over its service life, making it the worse choice for a light meter.

If your camera’s instructions call for an SR44, you should use an SR44 and not replace it with an LR44. The small price difference is easily offset by the significantly more accurate exposure metering.

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

There are two proper ways to use an SR44 in a PX625 camera anyway: First, a PX625 adapter with a Schottky diode, which reduces the voltage and compensates for the mechanical difference. However, the battery check does not work reliably in this setup. Second, if your camera has what is known as a bridge circuit (e.g. Pentax Spotmatic), the camera electronics compensate for the voltage difference automatically. In that case, a purely mechanical adapter without a diode is sufficient.

A light meter does not measure light directly; it interprets the voltage at its input terminals as a measure of light intensity. If this voltage changes over the battery’s service life, the measured value also changes, even when the actual light remains the same. Excessive voltage (alkaline 1.5 V instead of the expected 1.35 V) causes underexposure, because the camera assumes there is more light than there really is and closes the aperture; too low a voltage causes overexposure. Negative film tolerates overexposure much better than underexposure, so a slight undervoltage is generally the lesser evil.

However, more important than the absolute value is consistency: Alkaline cells such as the LR44 continuously drop from 1.5 V to around 1.0 V and deliver fluctuating readings over their service life. Silver oxide (SR44), by contrast, maintains its 1.55 V almost steadily over around 90% of its discharge. That is why it was the natural successor to the mercury cell in the 1970s for all cameras designed at the factory for 1.5 V. Zinc-air and NiMH cells behave similarly consistently and are the cleaner options for historic 1.35 V cameras.