Battery type PX24: Compatible cameras

The PX24 (also Eveready 532, V24PX, A24PX, EPX24, or 2LR50) is a cylindrical 3.0-volt alkaline battery consisting internally of two 1.5 V alkaline cells connected in series. It has two large push-button contacts (snap connectors) at both ends and measures approximately 16.8 × 42.4 mm. From the 1960s onward, it was manufactured by Mallory, Eveready, Varta, and Duracell; today, it is still available as a specialty battery from Exell (A24PX/532). Important: Unlike the better-known PX625 or PX27, the PX24 is not a mercury cell. It was an alkaline battery from the outset and therefore is not covered by the mercury bans in the EU Batteries Directive 2006/66/EC.

The PX24 was used mainly in Polaroid Land cameras with pack film from the late 1960s and 1970s. The most important models are listed on this page: Polaroid Colorpack M6, Countdown M60, Countdown M80, and "The Clincher". Many other Polaroid Automatic and Countdown models also use the PX24, with one battery, for example Automatic 103, 104, 125, 135, 210, 215, 315, 320, 330, 420, 430, 440, as well as Countdown 70 and M60; with two batteries (one for the shutter and one for the development timer), Automatic 335, 350, 360, 450, as well as Countdown 90 and M80. Important: The similarly named Polaroid Automatic 100, 240, and 250 do NOT require the PX24/532, but the PX19/531 at 4.5 V. This is a common confusion.

Original PX24 batteries are no longer produced by mass-market manufacturers. However, they are still available in two variants:

• Special reissue (Exell A24PX / 532): The US manufacturer Exell Battery still produces the original form factor as an alkaline battery. Available from photography specialists and online retailers, though usually at a significantly higher price than standard batteries.
• Battery adapter with standard button cells: An adapter in the PX24 format that holds two commercially available 1.5 V button cells (LR44/SR44) internally and features the correct snap contacts. Advantage: inexpensive, permanently available for repurchase, with standard batteries available everywhere. Available from Ausgeknipst as the PX24/532 3V adapter.

Several options are available for the PX24, each with its own strengths and weaknesses:

• Exell A24PX (original form factor): Direct replacement in the original format, alkaline chemistry, 3.0 V. Plug and play without an adapter, but relatively expensive and less commonly available. Disadvantage, as with any alkaline battery: the voltage continuously drops as the battery discharges.
• PX24 adapter with 2x LR44 (alkaline): Inexpensive, standard batteries available everywhere, with a nominal voltage of 3.0 V. Disadvantage: continuously declining voltage; as soon as the cells become weak, the reading fluctuates.
• PX24 adapter with 2x SR44 (silver oxide): Higher capacity than LR44, a significantly more stable discharge curve, and a nominal voltage of 3.1 V. Slightly more expensive than LR44, but clearly the better choice for the light meter because the voltage remains constant over almost the entire service life.
• 3 V lithium cell (CR type) in an adapter: Very long shelf life (~10 years), exactly 3.0 V, extremely flat voltage curve. Disadvantage: the form factor only fits special adapters, and not every Polaroid Land has enough room for a larger CR cell.

In Polaroid Land cameras with electronic automatic exposure, a voltage higher than the target 3.0 V causes the CdS light meter to register more light and open the shutter for a shorter time. This results in slight underexposure. Conversely, voltage that is too low leads to overexposure. However, the exposure electronics in pack-film Land cameras are relatively tolerant: fluctuations between 3.0 V (2x LR44) and 3.1 V (2x SR44) generally remain within the film's tolerance in practice. Like color negative film, Polaroid pack film tolerates overexposure better than underexposure, so slight undervoltage tends to be the lesser evil.

However, even more important than the absolute voltage is its consistency throughout the discharge curve: alkaline cells (including the original PX24) gradually lose voltage and provide fluctuating readings over their lifespan. Silver oxide (2x SR44) maintains a stable voltage over almost the entire discharge and is therefore the technically soundest choice for any older camera with automatic exposure, regardless of whether the original used a mercury or alkaline cell.