Garmin Tactix Delta Solar Replacement Battery 3.7V 300mAh

Garmin Tactix Delta Solar / Fenix 6X — 3.7V Li-Polymer Replacement Battery (361-00126-00)

This 3.7V, 300mAh Li-Polymer cell replaces the OEM battery in the Garmin Tactix Delta Solar, Fenix 6X, and Fenix 6X Pro Solar. All three watches use the same 361-00126-00 cell on a shared board layout with an identical connector and BMS handshake. Dimensions are 36.00 × 24.80 × 4.00mm — verify your original cell before fitting.

• Tactix Delta Solar, Fenix 6X, Fenix 6X Pro Solar: These models share the same battery bay dimensions, the same 3-pin flex connector, and the same fuel gauge IC. One cell covers all three — no wiring adapters or firmware differences to work around.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on a Fenix 6X board. The BMS accepted the cell cleanly, the fuel gauge initialised without fault codes, and solar charging resumed normally once the watch was placed under a charge source.
• Post-swap charging on the Tactix Delta Solar: The solar charging layer on the Tactix Delta Solar adds a trickle input to the charge circuit. After fitting this cell, connect the watch to its magnetic USB charger — not just sunlight — and run a full charge to 100%. The solar input alone will not trigger a proper fuel gauge calibration cycle after a cell swap.

Why the Tactix Delta Solar reads incorrect battery percentage after a cell swap

The Tactix Delta Solar uses a coulomb-counting fuel gauge IC that tracks charge state against a stored reference. When the cell is removed, that reference is lost. The IC wakes up with the new cell and has no baseline to work from, so it reports an arbitrary or incorrect percentage. A full charge cycle from near-zero resets the reference and restores accurate readings. Until that cycle completes, percentage figures are unreliable — do not rely on them to judge whether the swap worked.

Magnetic charge contacts not making after reassembly

If the watch does not respond to the magnetic charger after a battery swap, the charge contacts on the case back have likely shifted slightly during reassembly. Press the charger puck firmly against the rear contacts and rotate it a few degrees in each direction while watching for the charging indicator. If no indicator appears, remove the case back, check that the contact pads are seated flat, and reseat the back cover before retrying. The puck needs metal-to-metal contact across all four pins — even a 1mm misalignment breaks the circuit.