Olympus OM-1 Mercury Battery Replacements
The Olympus OM-1 originally used a 1.35V MR-9 mercury battery, which has been banned.
Mercury is terrible for the environment. If you have a mercury battery that was left in the camera, please dispose of it properly.
There are three types of batteries that can be used as replacement. Each has trade offs.
| Battery Type | Voltage | Stability | Availability |
|---|---|---|---|
| Zinc-air | 1.35V | High | Limited |
| Silver oxide | 1.5V | High | High |
| Alkaline | 1.5V | Moderate | High |
There are 386/SR43W silver oxide battery to MR-9 adapters available. They are a good option for gear enthusiasts.
It is also possible to modify the battery circuit of the OM-1 with a Schottky diode. This will drop the voltage from a silver oxide or alkaline battery to 1.35V.
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Zinc-Air Batteries
The WeinCELL MRB625 is a zinc-air hearing aid battery that produces 1.35V. That makes them perfect drop-in replacements.
No camera modification is needed for the light meter to work correctly.
They have a fixed lifespan as they react with air. As soon as the tab is pulled off, the countdown starts. Expect to have to frequently replace them.
These are harder to find and slightly more expensive than the other options.
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Silver Oxide Batteries
Silver oxide batteries produce 1.5V instead of 1.35V. Unless a camera has been modified, these will cause the light meter to slightly underexpose images.
The nice thing about these batteries is that they maintain a stable voltage as they drain. The amount photos are underexposed should be consistent through use.
The difference is easy to compensate for. Take a meter reading with another camera or phone. See how many stops the OM-1 is off. Then compensate by adjusting the film ASA speed by the same amount.
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Alkaline Batteries
These are the cheapest and easiest to find. They’re also the worst.
They produce 1.5V, but the voltage is not constant. A fresh battery can have a voltage over 1.7V. This could cause the light meter could underexpose by up to 2 stops.
As the battery drains, the voltage will decrease. For a short time, when the battery is around 1.35V, the camera will meter correctly. However, I would expect the battery to be almost completely drained.
Voltages lower than 1.35V will cause images to be overexposed.
The voltage should not change much if casually shooting on a single day. You can reference a light meter reading from your phone to see how far the camera is off. Then compensate by changing the film ASA/ISO.
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How to Perform a Battery Check
The battery check button is located on the front of the camera, to the right of the lens.
When you press this button, the needle in the viewfinder should move to the “BC” mark if the battery is good.
If the needle doesn’t move to the “BC” mark, it’s time to replace your battery.
You can find a scan of the Olympus OM-1 Manual from butkus.org.
MR-9 Battery Adapters
The “real” adapters have built-in electronics to drop the voltage on a 386/SR43W silver oxide battery to 1.35V.
There are lots of “knock-offs” that are just battery holders. It’s paying to be able to use a more expensive smaller capacity battery.
I only think these make sense for an enthusiast that is going to be using many different camera bodies. For casual use, zinc-air batteries are hard to beat.
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Schottky Diode Modification
If you know basic electronics and have the ability to solder, the modification is straight forward.
- Remove the bottom plate.
- Find the positive battery wire.
- Solder a Schottky diode with a voltage drop of 0.15V inline with the circuit.
- Make a note of the modification on the camera. (Film canister compartment)
Using the Olympus OM-1 Without a Battery
The OM-1 has a mechanical shutter. It does not need a battery for the shutter to fire.
The battery only powers the light meter. A handheld light meter could be used, like the Pentax Spotmeter V
Cleaning Battery Corrosion
Battery corrosion can easily be cleaned with distilled white vinegar. Dampen a cloth of cotton swab and rub the affected area.
The area can further be cleaned with rubbing alcohol. This will remove any contaminants which will prevent further corrosion.
Remove batteries from cameras when storing them. This will prevent a leaking battery from ruining a camera.