Which battery replaces the PX32?

The PX32 is a 5.6-volt mercury battery, internally constructed as a stack of four 1.35 V mercury cells (designation HM-4N: "4 Hg cells"). From the late 1960s onward, it was manufactured by Mallory (as TR164), Eveready (E164), and Varta (V164PX), among others, primarily for the Yashica Electro 35 family. Dimensions: approximately 16.5 mm in diameter × 45 mm in length, significantly larger than today’s 6 V button batteries. Like all mercury cells, it delivered a constant voltage over almost the entire discharge, making it ideal for the electronically controlled shutter speeds of the Electro 35.

The primary users were the entire Yashica Electro 35 rangefinder series: Electro 35, GS, GT, GSN, GTN, GTS, GL, AX, Electro G, Electro Half, the Gold Mecanica variants, as well as the later Kyocera-labeled models (35G, 35GL, 35GS, 35GSN, 35GT, 35GTN). Also the Yashica MG-1, the Konica Electron rangefinder camera, and the Sekonic light meters L-256 and L-258. You can find the complete searchable list with all 26 models at the top of this page.

Mercury-containing batteries such as the PX32 were banned in the EU under Battery Directive 2006/66/EC; in the USA, a comparable ban has been in force since 1996 under the Mercury-Containing and Rechargeable Battery Management Act. The last legally available stocks were used up around 2009. The reason is not the battery itself, but the environmental impact of mercury when improperly disposed of. The voltage-stable properties that made them technically so popular are now available only indirectly, through zinc-air or NiMH replacement solutions.

There is no single “best” replacement; each option has its own strengths and weaknesses:

• 4LR44 (6 V alkaline) in an adapter: Standard solution. The 4LR44 is an inexpensive, widely available stack battery (e.g. for dog collars), is approximately 25 mm high, and is extended to the PX32's 45 mm length using an adapter. Available from Ausgeknipst as the PX32 adapter incl. 4LR44 battery. Advantage: inexpensive and readily available for repurchase. Disadvantage: alkaline voltage drops slightly over the battery's lifetime.
• 4SR44 (6.2 V silver oxide) in the same adapter: Drop-in replacement of the alkaline cell with a silver-oxide cell. Higher cost, but a significantly more consistent voltage curve throughout its service life and a longer shelf life. For heavily used Yashica Electro 35 cameras, this is the technically cleaner setup.
• Four stacked LR44/SR44 cells instead of a 4LR44: This also works mechanically, but is fiddly (four loose button cells have to be stacked with the correct polarity) and costs about the same as a ready-made 4LR44. Only as a temporary solution if no 4LR44 is available.
• Original PX32 / TR164 / E164: Old stock is occasionally offered on eBay. However, the cells have often leaked or been deeply discharged, and the sale of new mercury-containing cells in the EU is prohibited. Not recommended.

For the Yashica Electro 35 family, generally no, and that is the key distinguishing feature here compared with other mercury cameras. The Electro 35 uses a bridge circuit in its light meter that automatically compensates for voltage fluctuations over a wide range. A 4LR44 (6 V) or 4SR44 (6.2 V) therefore provides readings that, in practice, do not differ from those of the original 5.6 V mercury cell. That is precisely why the 4LR44 is the pragmatic standard replacement here.

In theory, the usual principle applies: higher voltage makes the light meter assume there is too much light, leading to underexposure; lower voltage leads to overexposure. Negative film tolerates overexposure much better than underexposure, so slight undervoltage would generally be the lesser evil. More important than the absolute value is the consistency throughout the discharge curve: alkaline cells such as the 4LR44 gradually lose voltage, while silver-oxide cells (4SR44) maintain a much more stable voltage. In the Electro 35, both are uncritical thanks to the bridge circuit, but with finicky light meters such as the Sekonic L-256, the 4SR44 is the technically cleaner choice.