Garmin Fenix 7S Replacement Battery 3.85V 210mAh

Garmin FENIX 7S / Venu 2 — 3.85V Li-Polymer Replacement Battery (361-00139-10)

This 3.85V, 210mAh Li-Polymer cell replaces the original battery in the Garmin FENIX 7S and Venu 2 smartwatches. Both watches run the same compact 28.00 × 20.00 × 3.30mm cell with identical connector pinout and BMS voltage thresholds. Capacity is rated at 0.81Wh, matching the OEM specification.

• FENIX 7S and Venu 2 shared cell: Both watches share the same physical footprint, flex connector, and 3.85V charge termination voltage. Swapping this cell into either model requires no modification to the connector or ribbon routing.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on a FENIX 7S unit. The BMS accepted the new cell without fault codes, and charge termination triggered correctly at 4.35V. Fuel gauge IC re-calibrated after a full charge cycle from near-zero.
• Post-swap charging on FENIX 7S and Venu 2: Place the watch on its magnetic charger immediately after fitting the new cell and charge to 100% before first use. The fuel gauge IC on both platforms loses its state-of-charge reference when the cell is disconnected. Without a full charge cycle from near-zero, the percentage readout will be inaccurate and the watch may shut down unexpectedly at reported mid-charge levels.

Why the FENIX 7S reports wildly wrong battery percentages after a cell swap

The FENIX 7S uses a fuel gauge IC that tracks charge by integrating current over time. When the cell is physically removed, that running total resets to zero with no reference point. The IC then estimates state-of-charge based on open-circuit voltage, which is unreliable on a fresh cell that has not been fully cycled. One full charge to 100% followed by normal use gives the IC enough data to re-anchor its calculations. After that first cycle, percentage readings stabilise.

Magnetic charger not registering contact after reassembly

The FENIX 7S charges through four exposed pogo-pin contacts on the case back. If the rear housing shifts slightly during reassembly, the charger's magnet may still snap into place but the pins may not align with the watch contacts. Check that the charger sits flush with no visible gap on any edge. Clean both contact surfaces with a dry cloth to remove any adhesive residue from the battery swap. Correct alignment shows a charge indicator on screen within five seconds of docking.