Suunto 9 Smartwatch Replacement Battery 3.8V 290mAh

Suunto 9 / 9 Baro — 3.8V Li-Polymer Replacement Battery (175-8141)

This 3.8V, 290mAh lithium-polymer cell replaces the original battery in the Suunto 9 and Suunto 9 Baro GPS smartwatches. It fits the 28.20 × 26.00 × 4.00mm cavity and connects to the same BMS board used across both variants. Capacity figure is taken from product data: 290mAh / 1.1Wh.

• Suunto 9 and 9 Baro platform: Both models share the same 3.8V cell format, connector pinout, and BMS handshake logic, which is why one cell covers both. The barometric altimeter in the 9 Baro adds a continuous pressure-sensor draw that the BMS accounts for in its discharge curve.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on the Suunto 9 platform. The BMS accepted the cell without error flags, fuel gauge re-calibrated after a full charge-to-discharge pass, and GPS acquisition held stable throughout.
• Post-swap charge requirement: After fitting this cell, place the watch on its magnetic charger immediately and charge to 100% before first use. The fuel gauge IC on this platform loses its reference point when the cell is swapped — it cannot recalibrate without a full charge cycle from near-zero.

Why the Suunto 9 drops to 0% immediately after a battery swap

The Suunto 9 uses a coulomb-counting fuel gauge IC that tracks remaining capacity relative to a stored reference. When the cell is removed, that reference is lost. The IC has no baseline for the new cell, so it defaults to 0% or shuts down entirely at first power-on. This is not a fault with the replacement cell. A full charge cycle from near-zero re-establishes the reference and returns accurate percentage readings.

Watch not pairing with phone after battery replacement

Removing the battery terminates any active Bluetooth Low Energy session stored in the watch's RAM. When the device powers back on, the pairing record on the watch side can become mismatched with the phone's stored bond. The fix is to remove the Suunto app's device entry on the phone, delete the watch from the phone's Bluetooth settings, and re-pair from scratch. On iOS, go to Settings → Bluetooth → forget the device before reopening the Suunto app.