Canon F-1 (Classic): Replacing the battery — PX625 alternative with Type-675 hearing aid batteries and O-ring adapter

Summary

The classic Canon F‑1 originally uses mercury batteries (PX625), which are no longer available. But don't worry: a practical, environmentally friendly and inexpensive alternative are Type 675 zinc-air hearing aid batteries together with a small spacer (rubber O-ring) or a professional PX625 Adapter. These provide a constant voltage close to 1.35 V and your exposure metering will work like new again.

Why the old batteries are a problem

Many analog cameras used to run on mercury batteries. The ingenious thing about them was their extremely constant discharge voltage, which is why many light meters are calibrated exactly to them. But since mercury batteries are now banned and hardly available anymore, you need a replacement that delivers exactly the same electrically.

Why Type 675 (zinc-air) is a good choice

• The nominal voltage under load is about 1.35–1.4 V — that's damn close to the old PX625/mercury voltage.
• Zinc-air batteries have a relatively flat discharge curve, which keeps your light meter stable.
• They are completely mercury-free and much more environmentally friendly than the old PX types.

What you need

• Canon F‑1 (Classic) with intact battery compartment
• Type 675 zinc-air hearing aid battery (available from various manufacturers)
• Small rubber O-ring as a spacer or a suitable PX625 Adapter
• Contact cleaner and possibly a small tool (coin for opening, fine blade or screwdriver for cleaning)

Step-by-step: Replacing the battery

1. Open the lid: Unscrew the battery compartment cover on the bottom of the camera with a coin.

1. Check and clean the contacts: Old contacts are often a bit oxidized. If they look heavily soiled, carefully brush them off with a small screwdriver or a fine blade and then go over them with some contact cleaner.

1. Remove the old battery: Take out the old battery. Be sure to check for residue or corrosion in the compartment.

1. Activate zinc-air battery: These cells react with air. After removing the protective tab, the battery sometimes needs 1–2 minutes until the full voltage is stable. So wait a moment before continuing.

1. Attach spacer / O-ring: The Type 675 cells are slightly smaller than the original PX625 and would wobble in the compartment. Use a small rubber O-ring as a spacer: Simply slide it onto the battery so that it fits snugly and makes contact.

1. Note the polarity & insert: The positive side (plus) goes up — put it in, close the compartment and tighten the lid again.

Practical tips

• If the exposure metering seems strange after installation, first check the contacts and the voltage of the new battery.
• Zinc-air batteries discharge faster if they are permanently exposed to air. It is best to store unused cells with the protective tab or in the original packaging.
• Remove the batteries if you are not using the camera for an extended period of time to avoid damage from leakage or aging.
• The rubber O-ring is often the easiest DIY solution; however, there are also special PX625 Adapter made of metal, which are even more durable.

Safety and disposal

Even though zinc-air batteries do not contain mercury, they do not belong in household waste. Please dispose of used cells properly — simply return them to the battery collection point at the store or at your collection point.

Conclusion

For the Canon F‑1 (Classic) are type 675 batteries together with an O-ring or adapter an ingenious, inexpensive solution to replace the old mercury cells. They deliver the correct voltage, protect the environment and your light meter continues to work precisely.

Good luck with the change — and "good light"!

Yours, Vladi