The SR512SW, retail number 335, is an extremely thin 1.55 volt silver-oxide cell: 5.8 mm across and only 1.25 mm tall, with roughly 6 mAh of capacity. It exists for ultra-slim watch movements where even a standard small cell is too thick.
SR512SW, face and side profile, drawn to scale: 5.8 mm across, 1.25 mm thick.
Voltage
1.55 V
Size (D×H)
5.8 × 1.25 mm
Chemistry
Silver oxide (Ag2O)
Capacity
6 mAh
Same battery, other names
Every code below is the exact same cell as SR512SW. Any of them will fit and work identically.
335
Buying and replacement notes
At 1.25 mm this is about the thinnest silver-oxide cell in common circulation, and its capacity is correspondingly tiny. It has no alkaline or lithium substitute. Buy from a source with fresh stock, because a 335 that has sat on a shelf for years has lost a meaningful share of its 6 mAh to self-discharge.
⚠️ Keep away from children. Swallowed button batteries, especially 20 mm lithium coins, cause severe injury within hours. If a child swallows one, call the 24/7 National Battery Ingestion Hotline (US) at 800-498-8666 or poison control at 800-222-1222 immediately. What every parent should know.
Frequently asked questions
What is a 335 battery equivalent to?
Only the SR512SW; they are two names for the same 5.8 x 1.25 mm silver-oxide cell. Nothing else matches its thickness, so there is no cross-chemistry substitute. Murata, Renata and Seizaiken all manufacture it under these codes.
Why does my slim watch use such a rare battery?
Thin dress watches use movements only a couple of millimeters thick, and the battery must fit inside that. The 335's 1.25 mm height is the enabling dimension. The trade-off is capacity: about 6 mAh, which still runs an efficient movement for one to two years.
Can I stretch battery life in a watch that takes a 335?
Keep the watch serviced and avoid leaving it stopped with a dead cell inside, which risks leakage damage. Pulling the crown to hack the movement during long storage stops the motor drain. Beyond that, life is set by the movement's current draw.