In short: The PX625 Universal Adapter (MR9 Adapter) lets you use inexpensive Type-675 zinc-air batteries instead of the discontinued PX625 mercury cell. Under the low load of a CdS meter, Type 675 stabilizes at ~1.35 V — exactly the original voltage of the PX625, so your light meter measures correctly again. Made from conductive plastic, the adapter contacts the battery from the side, bottom, and top. Compatible with Canon, Nikon, Minolta, Olympus, Pentax, Rollei, Praktica, and more.
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Original voltage without modification: Zinc-air batteries (Type 675) drop to ~1.35V under the minimal load of a CdS meter — exactly the voltage of the original PX625 mercury cell. Flat discharge curve without drift: your light meter measures correctly again.
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One adapter for all contact types: The conductive plastic establishes contact regardless of geometry — whether your camera contacts the battery from the side, bottom, or top. No trial and error.
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Runs on Type 675 batteries from the drugstore: Available at dm, Rossmann & Co. and online — in 6-packs for under 3 EUR, instead of a discontinued specialty cell.
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Ready to use immediately: 2 adapters + 6 batteries in the standard set — unpack, insert, shoot. No further purchases needed.
Compatibility
Fits various cameras, including:
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Canon: Canonet series (QL17, QL19, 28, G-III), F series (F-1, FT, FTb, FX), Demi / Dial series [...]
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Nikon: F series (F, F Photomic, FTN), Nikkormat / Nikomat series (FT, FTN) [...]
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Minolta: SR-T series (100-303, MC, SC, Super), SR series (1, 7, 100-505), Hi-Matic series (7, 7S, 9, 11) [...]
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Olympus: OM-1 series (OM-1, MD, N), 35 series (RC, RD, SP, DC), Pen series (F, FT, D2, EED) [...]
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Pentax: K series (K2, KM, KX), Spotmatic F, H series (H1a, H3v) [...]
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Rollei: 35 series (35, 35S, 35T, Classic), SL35 series (SL35, SL35M, SL350), XF35 / A26 [...]
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Praktica: MTL3, super TL / super TL 1000, MTL5, LTL / LTL3 [...]
Not sure if the battery fits your camera?
Here is a complete list of all cameras compatible with the PX625 battery type.
Contents
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Standard: 2x PX625 adapters, 1x battery pack (Type 675)
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Double pack: 2x standard sets (4x PX625 adapters, 2x battery packs Type 675)
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Set: Standard + 1x universal light seal set including mirror damper
Technical details
- 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
This PX625 adapter — also known as the MR9 adapter — replaces the PX625 mercury battery, which was standard in many analog cameras from the 70s to the 90s. Since the EU ban, there has been no direct replacement. Alkaline batteries (LR44) provide too high and fluctuating voltage. Silver oxide cells (SR44) are stable but also too high.
This adapter uses common hearing aid batteries of Type 675 — available at any drugstore (dm, Rossmann & Co.) and online, 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 taken from the top, bottom, or side.
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 under the minimal load of a CdS meter to ~1.35V — 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 this solution: Type 675 hearing aid batteries are available everywhere — drugstores, pharmacies, online — and cost a fraction per piece.
Practical tips
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Activation: After removing the protective foil, wait 1–2 minutes before inserting the battery. The cell needs oxygen to activate.
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Storage: Unopened batteries last 2–3 years. Only remove the foil when you actually need the battery.
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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 when the battery is full. This is normal — the light meter still works correctly.
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Replenishment: Type 675 batteries are available at any drugstore (dm, Rossmann & Co.), pharmacies, and online. You’re not tied to a specialty supplier.
Frequently asked questions
“Zinc-air dries out — they only last a few weeks”
Correct: 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 makes the batteries last 2–3 months. At a unit price under 0.50 EUR, this is an acceptable tradeoff.
“1.4V is not 1.35V — will my light meter 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 ~1.35V. The deviation from the original is at most 0.05V — about 1/3 stop. Negative film tolerates 3–5 stops of overexposure without visible quality loss. For 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 for camera use. 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 causes 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 measurement results unpredictable. Silver oxide (SR44, 1.55V) is more voltage-stable but still too high. The adapter with zinc-air is the only passive solution that provides the correct voltage.
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.
Want to learn more about voltage and light metering?
In our FAQ article on batteries and adapters for analog cameras, we explain all alternatives in detail — including voltage comparisons and when each solution is right.
