Film cameras
Olympus OM-1 battery
1 × 1.35V mercury (legacy) button cell
The Olympus OM-1 meter was designed for a 1.35V mercury PX625 (also PX13 / MR9). Modern options include Wein MRB625 zinc-air or an MR-9 adapter with silver-oxide 386 / SR43W. Alkaline 1.5V lookalikes can fit and still meter wrongly. The shutter is mechanical — only the meter needs a cell.
How to replace it
| Compartment | Battery chamber for the CdS meter (base / front chamber depending on OM-1 vs OM-1n) |
|---|---|
| How to open | Open the meter battery cover; insert a 1.35V-class PX625 replacement (zinc-air or adapter path). Match polarity marks. |
| Orientation | Follow polarity marks in the chamber |
| Low battery indicator | Meter needle behaviour becomes unreliable when the cell is weak |
| Notes | Shutter is mechanical — the camera can expose without a meter cell. The meter needs a live 1.35V-class cell. |
| Access | Tool-free |
Important
- Meter was designed for 1.35V mercury PX625 / PX13 / MR9 — not a 6V AE-1 / 4LR44 cell.
- Alkaline LR9 / 1.5V “PX625” lookalikes can fit and still meter wrongly because voltage and discharge curve differ.
- Common modern options: Wein MRB625 zinc-air, or an MR-9 adapter with a silver-oxide 386 / SR43W cell.
- Mechanical shutter works without a battery; only the meter needs power.
- Keep button cells away from children.
Sources
Helpful for this device
Optional tools for opening, testing or charging — separate from the battery answer.
- Fluke 101 Digital Multimeter
Accurate open-circuit voltage and basic electrical checks
- Klein Tools MM400 Multimeter
General DC voltage checks including battery terminals
- Digital multimeter
Measure open-circuit voltage and general electronics checks
New battery but still not working?
A fresh 1 × PX625 should restore Olympus OM-1 if the battery was the problem. Work through the checks below before replacing the device.
- Check orientation
Confirm the cell is seated correctly: Follow polarity marks in the chamber
- Check the battery type
This device needs 1 × PX625 (mercury_oxide_legacy). Rechargeable cells are not supported for this device. Same size does not always mean the same battery.
- Check known model-specific issues
Meter was designed for 1.35V mercury PX625 / PX13 / MR9 — not a 6V AE-1 / 4LR44 cell. Alkaline LR9 / 1.5V “PX625” lookalikes can fit and still meter wrongly because voltage and discharge curve differ. Common modern options: Wein MRB625 zinc-air, or an MR-9 adapter with a silver-oxide 386 / SR43W cell.
- Confirm the battery itself
Try a known-good fresh cell of the exact code listed above.
- Still not responding?
If a correct, fresh battery installed properly does not restore the device, the fault may be elsewhere — the device may need service or replacement.