SR44 / CR1/3N Battery: Compatible Cameras

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

This format is used mainly in the later generation of Leica cameras, in both the M line and the electronic R series. Specifically: Leica M6 Classic, Leica M6 TTL and Leica MP, plus 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 powers the shutter as well. The Leica R7 doesn't belong on this list: it runs on a 6-volt system and needs 4× SR44 or 2× CR1/3N. You'll find the full searchable compatibility list at the top of this page.

Electrically, both options work perfectly well in the cameras listed. Which one you go for is a trade-off:

• 2× SR44 silver oxide: These cells are the historical benchmark for analog light meters. Silver oxide holds its voltage almost perfectly steady at 1.55 V per cell until shortly before the end of its life. Typical capacity is around 150 to 200 mAh, and meter readings are very precise. Downside: you have to stack two cells and insert both the right way round, which makes changing them a bit more fiddly. Available from Ausgeknipst as a 4-pack SR44 refill.
• 1× CR1/3N lithium: One cell instead of two, so it's quicker to change and there's less chance of a stacking mistake. Lithium has very low self-discharge (10+ years shelf life) and works reliably in the cold too, which makes it a good choice for occasional use and shooting outdoors. Downside: at the end of its capacity, lithium drops off more abruptly than silver oxide, and local drugstores/supermarkets are less likely to stock the CR1/3N than the SR44 (though it's easy to get online). Brands: Varta, Duracell, Panasonic.

With 2× SR44, both cells have to be stacked with the plus side facing up. In other words, the larger flat side (plus) faces the positive terminal of the battery compartment, usually upwards or towards the screw cap. If the cells are stacked pole to pole (plus against plus), the voltages cancel each other out and the meter stays dead. With the single CR1/3N, plus is the flat main side and minus is the small negative ring on the opposite side. With either option, inserting the battery the wrong way round usually doesn't damage anything. The Leica circuits are protected against reverse polarity; the camera simply won't respond.

The Leica bodies covered here (M6, MP plus R-E and R4 to R6.2) were designed for 3 V from the factory, so both the silver oxide stack (3.1 V) and lithium (3.0 V) sit right within spec; models with a 6-volt system, such as the R7 or the M7, aren't covered here. With PX625 cameras it was exactly the other way round: they were built for 1.35 V mercury cells, and every modern replacement either runs too high (1.5 V alkaline) or has a different discharge curve. Even so, with SR44/CR1/3N: silver oxide holds its voltage very steadily over its entire life (historically the main reason this chemistry was preferred for light meters in the first place), and lithium is stable too, but drops off more steeply towards the end of its capacity. Alkaline button cells (LR44) are out of the question for accurate metering, because their voltage falls steadily 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.