About this replacement
Motorola Moto 360 2nd Generation — 3.8V Li-Polymer Replacement Battery (FW3S)
This is a 3.8V, 250mAh Li-Polymer replacement cell for the Motorola Moto 360 2nd generation smartwatch. It slots into the same footprint as the original FW3S cell at 27.30 x 25.70 x 3.75mm. Fit this battery when the original no longer carries the watch through a full day.
- Moto 360 2nd Gen platform fit: The FW3S cell runs a single voltage rail shared by the display driver, Snapdragon Wear processor, and Bluetooth radio. All three draw from the same cell — connector pinout and BMS handshake are unchanged from the factory cell.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on the Moto 360 2nd Gen board. The BMS accepted the new cell without fault flags, and the fuel gauge registered capacity correctly after a full charge from near-zero.
- Post-swap charging protocol: After fitting the new cell, place the watch on its magnetic charger immediately and bring it to 100% before wearing it. The MAX17048 fuel gauge IC on this platform loses its reference point when the cell is swapped — it cannot recalibrate without a full charge cycle starting from near-zero.
Why the Moto 360 2nd Gen shows 0% immediately after a battery swap
The Moto 360 2nd Gen uses a coulomb-counting fuel gauge that tracks charge state relative to a stored reference. Removing the original cell wipes that reference from volatile memory. When the new cell lands, the gauge has no baseline and defaults to 0% or shuts the display off entirely. This is not a fault with the replacement cell — it is the IC behaving correctly with no data. Place the watch on charge immediately after reassembly and let it reach 4.35V full charge before powering it on.
Watch not pairing to the Motorola Connect app after cell replacement
Pulling the battery cuts power to the Bluetooth controller and drops its active session with the paired phone. The phone-side Bluetooth stack still holds the old bond record, which blocks a clean reconnect. On the phone, go to Bluetooth settings, forget the Moto 360 completely, then re-pair from scratch through the Motorola Connect or Wear OS app. Do not attempt re-pair until the watch has completed its first full charge cycle post-swap.