Garmin Tactix Delta 3.7V 400mAh Compatible Battery 361-00126-00

Garmin Tactix Delta — 3.7V Li-Polymer Replacement Battery (361-00126-00)

This is a 3.7V, 400mAh Li-Polymer cell for the Garmin Tactix Delta smartwatch (010-02357-00). It replaces OEM part 361-00126-00. If your watch no longer holds a charge across multi-day GPS or tactical use, this is the cell to swap.

• Tactix Delta platform fit: The Tactix Delta uses a fixed connector pinout and a fuel gauge IC that tracks cell impedance over time. This replacement matches the original cell's dimensions (36.70 × 24.50 × 4.95mm), connector orientation, and impedance profile so the fuel gauge reads correctly after swap.
• Bench tested on actual hardware: We ran the cell through charge and discharge cycles on a Tactix Delta unit. The BMS accepted the new cell without error flags, and the fuel gauge IC settled to accurate readings after one full charge cycle from near-zero.
• Fuel gauge calibration after cell swap: Place the watch on its magnetic charger immediately after fitting this cell and charge to 100% before first use. The fuel gauge IC on the Tactix Delta loses its reference point when the original cell is removed — it cannot calibrate without a full charge cycle from near-zero post-swap.

Why the Tactix Delta battery meter reads incorrectly after a cell replacement

The Tactix Delta uses a coulomb-counting fuel gauge IC that builds a model of the cell's capacity over hundreds of cycles. When you remove the old cell, that reference is wiped. The new cell starts with no history, so the IC estimates state-of-charge from open-circuit voltage alone — which produces jumpy or inaccurate percentage readings. One full charge-discharge cycle from near-zero gives the IC enough data to recalibrate and display accurate percentages again.

GPS and always-on display draining the new cell in under a day

The Tactix Delta's always-on MIP display and continuous GPS polling together pull significantly more current than basic timekeeping — this is normal hardware behaviour, not a fault with the cell. If the watch drains faster than expected in the first week after swap, the fuel gauge IC is still building its impedance model against the new cell's profile. Disable always-on display and continuous heart rate monitoring temporarily, then re-enable after a full calibration cycle. If drain remains severe after that, check that GPS mode is set to GPS-only rather than multi-band in Settings → Activity Profiles.