Battery type SR44 / CR1/3N: Compatible cameras

There are two ways to provide the same 3-volt power supply for the light meter: either two stacked SR44 silver-oxide button cells at 1.55 V each (each measuring 11.6 × 5.4 mm, around 3.1 V combined) or a single CR1/3N lithium button cell with a nominal voltage of 3 V (also known as 2L76 or DL1/3N, measuring 11.6 × 10.8 mm). The CR1/3N was specifically developed as a 1:1 replacement for the SR44 stack, with the same diameter and the same overall height as two SR44 cells stacked on top of each other. Both variants fit in the same battery compartment.

This format is used primarily in the later Leica generation, both in the M series and in the electronic R series. Specifically: Leica M6 Classic, Leica M6 TTL and Leica MP as well as Leica R-E, R4, R4s, R5, R6 and R6.2. In the mechanical models (M6, MP, R6), the battery powers only the light meter; in the electronic R-series models, it also powers the shutter. The Leica R7 does not belong on this list: It uses a 6-volt system and requires 4× SR44 or 2× CR1/3N. You can find the complete searchable compatibility list at the top of this page.

Both variants work reliably in the specified cameras. Which one you choose is a trade-off:

• 2× SR44 silver oxide: These cells are the historical reference for analog light meters. Silver oxide keeps the voltage nearly linear at 1.55 V per cell until shortly before the end of its service life. Typically around 150 to 200 mAh capacity, with very precise readings. Disadvantage: two cells must be stacked and both inserted the right way around, which is a little fiddlier when replacing them. Available from Ausgeknipst as a 4-pack SR44 refill pack.
• 1× CR1/3N lithium: One cell instead of two, faster to replace, and less chance of a stacking error. Lithium has very low self-discharge (10+ years of storage life) and also works reliably in cold conditions, making it attractive for occasional use and outdoor shooting. Disadvantage: lithium drops more abruptly at the end of its capacity than silver oxide, and CR1/3N is less commonly stocked in local drugstores and supermarkets than SR44 (though it is readily available online). Brands: Varta, Duracell, Panasonic.

With 2× SR44, both cells must be stacked with the positive terminal facing upward. The larger flat side (positive) therefore faces the battery compartment's positive terminal, usually upward or toward the screw cap. If the cells are stacked terminal to terminal (positive against positive), the voltages cancel out and the exposure meter remains dead. With the single CR1/3N, the positive terminal is the flat main side, while the negative terminal is the small negative ring on the opposite side. With either configuration, incorrect polarity generally does not cause any damage. The Leica circuits are reverse-polarity protected; the camera simply does not respond.

The Leica bodies discussed here (M6, MP, and R-E and R4 through R6.2) were designed at the factory for 3 V, so both the silver-oxide stack (3.1 V) and lithium (3.0 V) are exactly within the specified range; 6-volt-system models such as the R7 or M7 are not included here. With PX625 cameras, the opposite was true: they were designed for 1.35 V mercury cells, and all modern replacement batteries either run too high (1.5 V alkaline) or have a different discharge curve. Nevertheless, with SR44/CR1/3N batteries, silver oxide maintains a very constant voltage throughout its entire service life (historically, this was the main reason this chemistry was preferred for light meters in the first place); lithium is also stable, but its voltage drops more sharply toward the end of its capacity. Alkaline button cells (LR44) are unsuitable for precise measurements because their voltage continuously drops from 1.6 V to 1.2 V; with slide film, the resulting exposure errors are visible. Negative film is more forgiving, but for correct readings, SR44 or CR1/3N is the proper choice.