Classic PX mercury cells and modern paths

1.35V meter class (PX625 / PX675 / PX400)

PX625 / PX13 / MR9 — common meter cell; modern Wein MRB625 or MR-9 + silver oxide. Alkaline LR9 lookalikes can fit and still meter wrongly.

PX675 / V76PX — related 1.35V mercury lineage; Wein MRB675 is a common zinc-air path. Not the same chamber as PX625, and not ZA675 hearing zinc-air without checking the device.

PX400 — smaller 1.35V mercury cell; Wein MRB400 is the usual zinc-air trade path.

6V photo tray (PX28 family)

Modern PX28 / 4SR44 (silver), 4LR44 / PX28A (alkaline), and PX28L / 2CR1/3N (lithium) share a ~13 × 25 mm tray — chemistry still differs. See PX28 vs 4LR44 vs PX28L.

Other photo stacks (PX32 / PX27 / PX23)

PX32 / HM-N / E164 — legacy ~5.6V mercury; modern alkaline A32PX / PX32A is the common Electro 35 path (device caveats apply).

PX27 / V27PX and PX23 / S23PX — specialist mercury photo cells. Use adapter/voltage guidance from the device or a trusted specialist; do not assume 4LR44 or PX28.

Safety

Do not seek genuine mercury cells as new stock. Prefer documented modern chemistries and adapters. Always confirm the empty chamber and the meter/camera manual before substituting.