Universal PX625 Battery Adapter MR9 Replacement – Fits Canonet, Nikon F, Yashica Mat & Praktica

• Accurate exposure values thanks to a constant 1.35V. Zinc-air batteries drop to about 1.35V under the minimal load of a CdS meter – the voltage of the original PX625 mercury cell. Flat discharge curve, no drift.
• Universally compatible thanks to conductive plastic. Works equally well in cameras with side, bottom, and top contacts. No guessing which adapter fits your camera.
• Affordable batteries, available everywhere. Hearing aid batteries type 675 are available at every pharmacy, drugstore, and online – in 6-packs for under 3 EUR.
• Ready to use immediately with 2 adapters + 6 batteries. Unpack the complete set, insert, and start shooting.

Why zinc-air instead of alkaline or silver oxide?

The problem with LR44 or SR44: Alkaline delivers 1.5V, silver oxide even 1.55V. In cameras with CdS light meters (Olympus OM-1, Minolta SRT, Canon FTb, Rollei 35), this leads to up to 2 stops underexposure. The camera thinks it’s brighter than it actually is.

Zinc-air batteries (type 675) start at 1.45V and drop to about 1.35V under the minimal load of a CdS meter – the voltage of the original PX625 mercury cell. The discharge curve is flat, just like mercury. No voltage fluctuations, no drift over the usage period.

There are also zinc-air cells made directly in the PX625 format (e.g., Wein-Cells) – technically the same chemistry as hearing aid batteries, just in a different casing. The advantage of our solution: type 675 hearing aid batteries are available everywhere – pharmacy, drugstore, gas station – and cost just a fraction each.

Included in delivery

• Standard: 2x PX625 adapters, 1x battery pack (type 675)
• Set: Standard + 1x universal light seal set including mirror damper
• Complete set: Set + 1x extra battery pack (type 675)

Technical specifications

• Material: Conductive technical plastic
• Compatibility: Replaces PX625 / MR-9 / PX13
• Battery system: Enables use of PR44 / 675 zinc-air (1.4V)
• Fit: Universal (side and bottom contact)

Description

PX625 mercury batteries were the standard in many analog cameras from the 70s to the 90s. Since the EU ban, there is no direct replacement. Alkaline batteries (LR44) deliver too high and fluctuating voltage. Silver oxide cells (SR44) are stable but also too high.

This adapter uses common hearing aid batteries type 675 – available at every pharmacy and drugstore, in 6-packs for under 3 EUR. The adapters are made of conductive plastic and therefore work in almost all cameras: regardless of whether the battery contact is on top, bottom, or side.

Typical concerns – and our answers

“Zinc-air dries out – they only last a few weeks”

True: After removing the protective foil, the cell starts working. In a hearing aid (constant high current consumption), a 675 cell lasts 5–12 days. In a camera, the consumption is orders of magnitude lower – a CdS light meter draws microamps, and only when actively measuring. This means the batteries last 2–3 months. At a unit price under 0.50 EUR, that’s an acceptable tradeoff.

“1.4V is not 1.35V – will my light meter then measure incorrectly?”

1.4V is the nominal voltage under standard load. Your camera’s CdS light meter draws so little current that the voltage drops to about 1.35V. The deviation from the original is at most 0.05V – roughly 1/3 stop. Negative film tolerates 3–5 stops of overexposure without visible quality loss. With slide film, 1/3 EV is hardly noticeable in practice.

“Can moisture from the zinc-air battery damage my camera?”

Zinc-air cells use atmospheric oxygen as the cathode and contain a small amount of electrolyte. The theoretical possibility of moisture release exists but is irrelevant in practice when used in cameras. Hearing aids sit directly in the ear canal and are much more sensitive to moisture than a camera battery compartment. Thousands of photographers have used this solution for years without problems.

“Why not just use an LR44?”

You can – but not without consequences. 1.5V alkaline on a CdS meter calibrated for 1.35V results in systematic underexposure. In some cameras, up to 2 stops. Also, alkaline voltage fluctuates strongly over its lifetime (1.6V fresh, 1.2V empty). This makes meter readings unpredictable. Silver oxide (SR44, 1.55V) is more voltage stable but still too high. The zinc-air adapter is the only passive solution that delivers the correct voltage.

Practical tips

• Activation: Wait 1–2 minutes after removing the protective foil before inserting the battery. The cell needs oxygen to activate.
• Storage: Unopened batteries last 2–3 years. Only remove the foil when you actually need the battery.
• Battery check: Some cameras (e.g., Olympus OM-1, Minolta SRT) have a battery test function calibrated exactly for 1.35V. This sometimes shows “weak” for zinc-air even though the battery is full. This is normal – the light meter still works correctly.
• Reordering: Type 675 batteries are available at every pharmacy, drugstore, and online. You’re not tied to a specialty supplier.

Want a rechargeable solution?

If you don’t want to change disposable batteries: We developed the PX625 rechargeable battery with USB-C charger (V80H). A NiMH battery with 1.25–1.30V operating voltage, rechargeable via USB-C. Buy once, use for years.

More about voltage and exposure metering?
In our FAQ article on batteries and adapters for analog cameras, we explain all alternatives in detail – including voltage comparison and when which solution is right.