Battery type PX32 — Compatible cameras

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"). It was manufactured from the late 1960s by, among others, Mallory (as TR164), Eveready (E164), and Varta (V164PX), primarily for the Yashica Electro 35 family. Dimensions: about 16.5 mm diameter × 45 mm length — significantly larger than today's 6-V button batteries. Like all mercury cells, it delivered a constant voltage over almost the entire discharge, which made it ideal for the electronically controlled shutter speeds of the Electro 35.

The main 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-branded 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 like the PX32 were banned in the EU by the Battery Directive 2006/66/EC; in the USA, a comparable ban has been in effect since 1996 through the Mercury-Containing and Rechargeable Battery Management Act. The last legal stocks were used up around 2009. The reason is not the battery itself, but the environmental pollution caused by mercury in improper disposal. The constant voltage characteristics that made them technically so popular are now only available 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 the adapter: Standard solution. The 4LR44 is an inexpensive, widely available stacked battery (e.g., for dog collars), about 25 mm high, and is extended to the 45 mm length of the PX32 via an adapter. Available at Ausgeknipst as PX32 adapter including 4LR44 battery. Advantage: cheap, always available. Disadvantage: alkaline voltage slightly drops over the lifespan.
• 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 over the entire lifespan and longer lasting. The technically cleaner setup for heavily used Yashica Electro 35.
• Four stacked LR44/SR44 instead of 4LR44: Also works mechanically but is fiddly (four loose button cells must be stacked with correct polarity) and costs about the same as a ready-made 4LR44. Only as an emergency solution if no 4LR44 is available.
• Original PX32 / TR164 / E164: Old stock is occasionally offered on eBay. However, the cells are often leaked or deeply discharged — and the sale of new mercury-containing cells in the EU is prohibited. Not recommended.

For the Yashica Electro 35 family, usually no — and this is the most important peculiarity compared to other mercury cameras. The Electro 35 uses a bridge circuit in the 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 the original 5.6 V mercury cell. That is exactly why the 4LR44 is the pragmatic standard replacement here.

The usual principle theoretically applies: higher voltage causes the light meter to assume too much light and leads to underexposure; lower voltage to overexposure. Negative film forgives overexposure much better than underexposure, so a slight undervoltage would generally be the lesser evil. Even more important than the absolute value is the consistency over the discharge curve: alkaline cells like the 4LR44 decline slowly, silver oxide (4SR44) maintains the voltage much more stably — thanks to the bridge circuit in the Electro 35, both are uncritical, but with picky light meters like the Sekonic L-256, the 4SR44 is technically the cleaner choice.