About this replacement
Garmin Forerunner 245 / 245 Music — 3.8V Li-Polymer Replacement Battery (361-00086-11)
This is a 3.8V, 170mAh Li-Polymer cell that fits the Garmin Forerunner 245 and Forerunner 245 Music GPS running watches. It replaces OEM part 361-00086-11 and sits behind the rear case on the same flex connector. Swap it when the original cell no longer holds a charge across a full training week.
- Forerunner 245 and 245 Music compatibility: Both variants use the same 29.30 × 20.00 × 3.30mm cell footprint, identical voltage rail, and the same BMS handshake on the flex connector. No firmware difference affects this cell — the Music model's storage draws from the same battery circuit.
- Bench tested on actual hardware: We ran this cell through the Forerunner 245's charge controller and confirmed the BMS accepted the new cell without fault flags. The fuel gauge IC re-registered correctly once a full charge cycle completed from near-zero.
- Post-swap charge requirement for Forerunner 245: After fitting the new cell, place the watch on its magnetic charger immediately and charge it to 100% before first use. The fuel gauge IC on this platform loses its reference point when the cell is swapped — it cannot recalibrate without one full charge cycle from near-zero. Skip this step and the percentage readout will be inaccurate for days.
Why the Forerunner 245 shows 0% immediately after a battery swap
The Forerunner 245 uses a coulomb-counting fuel gauge IC that tracks charge state relative to a stored reference. When the cell is removed, that reference resets to zero. The watch has no way to measure the new cell's actual charge on insertion — it just sees an unknown state and defaults to 0%. This is not a fault with the replacement cell. Place the watch on charge immediately after reassembly and let it reach 100% without interruption. Once that full cycle completes, the fuel gauge sets a new reference and percentage readings will be accurate.
Watch not pairing with phone after battery replacement
Removing the battery cuts power to the BLE radio and drops the active Bluetooth session entirely. The phone retains the old device record but the watch starts with no session state — the two sides no longer agree on pairing keys. Open the Garmin Connect app, go to your device settings, and remove the Forerunner 245 from the paired devices list. Then re-initiate pairing from the watch's Bluetooth menu. The re-pair takes under two minutes and restores full sync.