Garmin Tactix 7 Replacement Battery 3.7V 300mAh

Garmin Tactix 7 / fenix 7X — 3.7V Li-Polymer Replacement Battery (361-00147-10)

This is a 3.7V, 300mAh lithium-polymer cell for the Garmin Tactix 7 and fenix 7X smartwatches. It replaces OEM part 361-00147-10 and restores power to the display, GPS module, heart rate sensor, and onboard navigation functions. Physical dimensions are 36.50 × 25.20 × 4.30mm — measure your existing cell before ordering if you are unsure.

• Tactix 7 and fenix 7X compatibility: Both watches run the same power architecture — identical voltage rail, connector footprint, and BMS handshake protocol — so one cell covers both platforms without modification.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on the Tactix 7 platform. The BMS accepted the new cell without fault codes, and the fuel gauge IC re-calibrated correctly after a full charge cycle from near-zero.
• Post-swap charge requirement for the Tactix 7 and fenix 7X: After fitting this cell, place the watch on its magnetic charger immediately and charge to 100% before first use. The fuel gauge IC on these platforms loses its reference point when the cell is swapped and cannot recalibrate without a complete charge cycle from near-zero — skipping this step causes the watch to report inaccurate state-of-charge from day one.

Why the Tactix 7 reports 0% and won't boot after a cell swap

The Tactix 7 uses a coulomb-counting fuel gauge IC that tracks charge by measuring current flow over time. When the cell is removed, that running count resets to an undefined state. A new cell at partial charge gives the IC no valid baseline, so it defaults to 0% and the watch refuses to boot as a low-battery protection measure. The fix is straightforward: connect the magnetic charger immediately after reassembly and let it reach 100% uninterrupted. Once the IC completes a full charge sweep, it locks in the new reference and percentage readings return to normal.

GPS and always-on display draining the new cell faster than expected

A fresh lithium-polymer cell presents slightly different internal impedance than a worn cell, and the Tactix 7's power management firmware adjusts current draw accordingly during the first several charge cycles. GPS tracking and always-on display mode together represent the highest sustained current load this 300mAh cell will see — running both simultaneously will noticeably shorten the charge interval compared to watch-only or step-tracking mode. This behaviour typically stabilises after three to five full charge cycles as the cell's impedance settles. If drain remains excessive beyond that point, check that the always-on display setting has not been re-enabled after the swap, as it resets to on during some firmware re-initialisation events.