Renata 399 (SR927W) High‑drain Silver‑Oxide Watch Battery

The Renata 399 (SR927W) is a 1.55 V silver‑oxide button cell engineered for watches that demand short bursts of higher current—think chronographs, alarms, and backlight functions. It matches the SR927 size standard (9.5 mm diameter × 2.7 mm height) and delivers stable voltage under load.

Key Specs

Chemistry	Silver‑oxide (mercury‑free)
Nominal voltage	1.55 V
Size standard	SR927 (9.5 × 2.7 mm)
Drain profile	High‑drain (W)
Typical capacity	~45–60 mAh (varies with load and brand)
Operating temperature	About −10 to +60 °C (device‑dependent)
Compliance	Mercury‑free, RoHS

When to Choose This Cell

• Use if your watch/manual or caseback specifies 399, SR927W, SR927 (W), or codes like SB‑AP.
• Best for watches with chronograph, alarm/sound, or LED backlight where higher current is needed.

Avoid If

• Your device calls for 395 / SR927SW (low‑drain). Match W vs SW exactly unless the manufacturer states otherwise.
• You plan to substitute an LR927 (alkaline) cell—voltage sags faster and runtime is typically shorter.
• You need a rechargeable cell (this battery is not rechargeable).

Compatibility and Equivalents

Matches the SR927 high‑drain format. Common cross‑references include:

• 399, SR927W, SR927 (W)
• Brand codes such as: Renata 399, Energizer 399, Maxell SR927W, Sony SR927W, Panasonic SR927W, Varta V399, Seiko SB‑AP

Do not interchange with 395 / SR927SW (low‑drain) unless your device allows it.

Performance and Lifespan

• Typical watch runtime: about 1–3 years in analog chronograph/feature‑rich models. Heavy alarm/light use can shorten this to months.
• Shelf life: commonly up to 4–5 years when stored sealed at 50–77 °F (10–25 °C), low humidity.
• Voltage remains relatively flat through most of the discharge, helping maintain accurate timekeeping.

Installation and Handling Tips

• Confirm markings: look for 399 or SR927W inside the caseback or in the manual.
• Handle with non‑metal tweezers or gloved fingers to avoid shorting or contaminating the cell.
• Check polarity before seating; the + side usually faces up in watch holders.
• If water resistance matters, inspect/replace the caseback gasket and pressure‑test if applicable.
• Recycle the old battery; do not dispose of in household trash.

Alternatives

• Low‑drain counterpart: Renata 395 (SR927SW) for simple quartz movements without high‑current features—use only if specified.
• Alkaline look‑alike: LR927/AG7 is the same size but lower performance and shorter life; not recommended except as a short‑term emergency substitute.

Safety Notes

• Keep out of reach of children. Button cells pose an ingestion hazard. If swallowed, seek immediate medical attention or call the battery ingestion hotline (US: 800‑498‑8666).
• Do not recharge, crush, or incinerate. Avoid mixing old and new cells.
• Store in original packaging, away from metal objects and heat sources.

FAQ

What’s the difference between 399 and 395?

Both are SR927 size. 399 (SR927W) is high‑drain for features like chronographs; 395 (SR927SW) is low‑drain for simple quartz movements. Use the type specified by your watch.

Can I use an LR927 instead of a 399?

Not recommended. LR927 is alkaline with lower capacity and steeper voltage drop, which can cause shorter life and unreliable operation in high‑drain watches.

How long will a 399 last in my watch?

About 1–3 years in many analog chronographs. Frequent alarm/light use reduces runtime; simple timekeeping only may extend it.

Is the 399 rechargeable?

No. It is a primary (single‑use) silver‑oxide cell. Replace and recycle when depleted.

How should I store spare cells?

Keep unopened in a cool, dry place (50–77 °F / 10–25 °C), away from humidity and metal objects. Avoid freezing or high heat.