Garmin Fenix 5X Replacement Battery 3.8V 410mAh

Garmin Fenix 5X Series — 3.8V Li-Polymer Replacement Battery (361-00098-00)

This 3.8V, 410mAh Li-Polymer cell replaces the OEM battery in the Garmin Fenix 5X, Fenix 5X Running, and Fenix 5X Plus smartwatches. It matches the original cell dimensions at 27.40 x 25.26 x 5.00mm and uses the same OEM part number 361-00098-00. Swap this cell when your watch no longer holds a charge across a full GPS activity or drops percentage unexpectedly under load.

• Fenix 5X and 5X Plus compatibility: All three fit models share the same battery bay dimensions, connector pinout, and fuel gauge IC wiring. The 5X Plus adds barometric altimeter and mapping functions, but the cell voltage and capacity spec are identical across the group — one part number covers all three.
• Bench tested on actual hardware: We ran this cell through charge-discharge cycles on the Fenix 5X platform and confirmed the BMS accepted the cell without fault codes. The fuel gauge IC re-referenced correctly after a full charge cycle from near-zero following installation.
• Post-swap charging on the Fenix 5X: After fitting this cell, place the watch on its magnetic charger immediately and charge to 100% before using it. The Fenix 5X fuel gauge IC loses its reference point when the old cell is disconnected. Without that first full charge cycle, the percentage readout will be inaccurate and may read 0% even with charge present.

Why the Fenix 5X battery percentage jumps or drops erratically after a cell swap

The Fenix 5X uses a coulomb-counting fuel gauge IC that tracks charge in and out of the cell. When the old battery is removed, the IC loses its stored state-of-charge reference entirely. It then tries to estimate remaining capacity from open-circuit voltage on the new cell, which gives a rough and often wrong starting number. The fix is a single uninterrupted charge from near-zero to 100% — that gives the IC the boundary points it needs to recalibrate the percentage curve accurately.

Magnetic charger not registering on the Fenix 5X after reassembly

The Fenix 5X charges through four contact pads on the rear case that align with the magnetic charging cable. If the rear cover shifts even slightly during reassembly, those pads can sit off-axis from the charger pins, giving no charge indication on screen. Check that the rear case is fully seated and the four gold contact points are clean and unobstructed. Place the charger on the back, confirm the charging icon appears on screen within 10 seconds, then verify voltage input is present — if not, rotate the charger 180° and reseat it.