Canon · Film cameras
Canon FTb battery
1 × 1.35V mercury (legacy) button cell
The Canon FTb meter was designed for a 1.3–1.35V mercury PX625 (Mallory PX-625 / Eveready EPX-625). Modern options include Wein MRB625 zinc-air or an MR-9 adapter with silver-oxide 386. Alkaline 1.5V lookalikes can meter wrongly. This is not the AE-1 / A-1 6V 4LR44 cell. The shutter is mechanical — only the meter needs a cell.
How to replace it
| Compartment | Battery chamber in the camera base |
|---|---|
| How to open | Coin-slot cover: turn left to open; insert the mercury-class cell with the central contact facing inward; turn cover right to close. |
| Orientation | Central contact (+) facing inward — follow diagram on cover |
| Low battery indicator | Battery check: ASA 100 + shutter 1000, hold meter switch at C — needle should reach the index |
| Notes | Remove the cell for long storage. Wipe poles before insert. Not a 6V AE-1 / A-1 photographic stack. |
| Access | Coin or simple twist |
Important
- Meter was designed for a 1.35V mercury PX625 / PX13 / EPX-625 — not a 6V 4LR44 / PX28 (AE-1 / A-1).
- Alkaline LR9 / 625A 1.5V lookalikes can fit and still meter wrongly as they discharge.
- Common modern paths: Wein MRB625 zinc-air or MR-9 adapter with silver-oxide 386.
- 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.
- iFixit Opening Picks
Non-marring opening for tool-free / clip housings
- Fluke 101 Digital Multimeter
Accurate open-circuit voltage and basic electrical checks
- Digital multimeter
Measure open-circuit voltage and general electronics checks
New battery but still not working?
A fresh 1 × PX625 should restore Canon FTb if the battery was the problem. Work through the checks below before replacing the device.
- Check orientation
Confirm the cell is seated correctly: Central contact (+) facing inward — follow diagram on cover
- 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 a 1.35V mercury PX625 / PX13 / EPX-625 — not a 6V 4LR44 / PX28 (AE-1 / A-1). Alkaline LR9 / 625A 1.5V lookalikes can fit and still meter wrongly as they discharge. Common modern paths: Wein MRB625 zinc-air or MR-9 adapter with silver-oxide 386.
- 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.