Battery type SR44 / CR1/3N — compatible cameras

These are two ways to provide the same 3-volt power supply for the light meter: either two stacked SR44 silver oxide button cells each with 1.55 V (dimensions 11.6 × 5.4 mm each, together about 3.1 V) or a single CR1/3N lithium button cell with 3 V nominal voltage (also called 2L76 or DL1/3N, dimensions 11.6 × 10.8 mm). The CR1/3N was specifically developed as a 1:1 replacement for the SR44 stack — same diameter, same total height as two SR44 stacked. Both variants fit into the same battery compartment.

This format is primarily used in the late Leica generation — both in the M series and 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 operates with a 6-volt system and requires 4× SR44 or 2× CR1/3N. The complete searchable compatibility list is at the top of this page.

Both variants work electrically cleanly in the mentioned 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• 2× SR44 Silver Oxide: These cells are the historical reference for analog light meters — silver oxide maintains voltage almost linearly at 1.55 V per cell until near the end of its lifespan. Typically around 150 to 200 mAh capacity, very precise measurements. Downside: two cells must be stacked and both inserted the right way, which makes replacement a bit fiddly. Available at Ausgeknipst as a 4-pack SR44 refill pack.
• 1× CR1/3N Lithium: One cell instead of two — quicker to change, less chance of stack errors. Lithium has very low self-discharge (10+ years shelf life) and works reliably even in cold, making it attractive for rare use and outdoor use. Disadvantage: lithium drops off more abruptly at the end of capacity than silver oxide, and CR1/3N is less commonly stocked in local drugstores/supermarkets than SR44 (but easily available online). Brands: Varta, Duracell, Panasonic.

With 2× SR44, both cells must be stacked with the positive pole facing up — the larger flat side (plus) thus points to the positive pole of the battery compartment, usually upwards or towards the screw cap. If the cells are stacked pole to pole (plus on plus), the voltages cancel out and the light meter remains dead. For the single CR1/3N, plus is the flat main side, minus is the small negative ring on the opposite side. In both cases, incorrect polarity usually does no damage — Leica circuits are reverse polarity protected, the camera just won’t respond.

The Leica bodies discussed here — M6, MP as well as R-E and R4 to R6.2 — were designed from the factory for 3 V, so both the silver oxide stack (3.1 V) and lithium (3.0 V) are exactly within the target range; models with 6-volt systems like the R7 or the M7 are not meant here. For PX625 cameras, it was exactly the opposite: 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. For SR44/CR1/3N, however, the rule is: silver oxide maintains voltage very consistently over the entire lifespan (historically the main reason why this chemistry was preferred for light meters), lithium is also stable but drops off more steeply towards the end of 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 values, SR44 or CR1/3N are the clean choice.