About this replacement
Garmin Venu / Fenix 6S Pro — 3.8V Li-Polymer Replacement Battery (361-00086-12)
This is a 3.8V, 170mAh lithium-polymer cell that replaces the original battery in the Garmin Venu and Fenix 6S Pro smartwatches. It fits the same 30.50 × 19.50 × 3.20mm cavity and uses the same OEM part number 361-00086-12. If your watch no longer holds charge across a full day of normal use, this cell is the direct swap.
- Venu and Fenix 6S Pro compatibility: Both watches run the same 3.8V battery rail, share the same connector pinout, and use a compatible BMS handshake — which is why Garmin uses one cell part number across both platforms. The 170mAh capacity matches OEM exactly.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on a Venu unit. The BMS accepted the cell without fault codes, charge termination triggered cleanly at full voltage, and the fuel gauge IC updated correctly after one full charge cycle.
- 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 calibrate the state-of-charge display without a full charge cycle from near-zero after installation.
Why the Venu reads 0% immediately after a battery swap
The Venu uses a coulomb-counting fuel gauge IC that tracks charge by measuring current in and out of the cell. When you remove the old battery, the IC loses its stored reference entirely. A fresh cell at 3.8V open-circuit voltage gives the IC no usable baseline — it defaults to 0% or shuts down. This is not a fault with the replacement cell. Charge the watch fully to 100% straight after fitting, and the IC will re-anchor its calibration to that full-charge endpoint.
Charge contacts not making on the magnetic charger after reassembly
If the watch sits on its charger but shows no charging activity after a battery swap, the charge contacts on the rear case have likely shifted slightly during reassembly. The Venu's magnetic charger relies on precise contact alignment — even 0.5mm of displacement breaks the circuit. Remove the watch from the charger, reseat it slowly, and confirm the magnet pulls the watch squarely into position. If charging still does not start, check that the rear cover is fully pressed flush before placing on the charger again.