Motorola Moto 360 2nd Gen FW3L Replacement Battery 3.8V

Motorola Moto 360 2nd 2015 — 3.8V Li-Polymer Replacement Battery (FW3L / SNN5962A)

This 3.8V, 370mAh Li-Polymer cell replaces the original battery in the Motorola Moto 360 2nd Gen 2015 smartwatch. It fits the 42mm round-case model released in 2015 and restores power to the display, heart rate monitor, notifications, and Bluetooth connectivity. Dimensions are 32.80 × 27.45 × 4.25mm — match these before ordering if your watch has been previously repaired.

• Moto 360 2nd Gen 2015 fit: This generation uses a specific connector orientation and cell footprint tied to the 42mm case. The 2014 first-gen and 2015 46mm variant use different cells — confirm your model number before fitting.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on the Moto 360 2nd Gen platform. The BMS accepted the cell without fault codes, and the fuel gauge IC re-established state-of-charge tracking after a full charge cycle from near-zero.
• Post-swap charge protocol: After fitting this cell, place the watch on its magnetic charger immediately and charge to 100% before wearing it. The fuel gauge IC on this platform cannot set an accurate reference point without one full charge cycle from near-zero following a cell swap.

Why the Moto 360 2nd Gen reads wildly wrong percentages after a battery swap

The Moto 360 2nd Gen uses a coulomb-counting fuel gauge IC that tracks charge by measuring current flow from a known baseline. When you remove the old cell, that baseline is lost. The IC wakes up with the new cell and has no reference, so it reports whatever it last stored — often 0%, 1%, or a random mid-range figure. This is not a fault with the replacement cell. A single full charge cycle from near-zero re-anchors the IC and percentage readings stabilise within 24 hours of normal use.

Magnetic charger not registering after reassembly

The Moto 360 charges through a magnetic pogo-pin cradle that requires the watch to sit flush and centred. If the rear cover was shifted even slightly during reassembly, the charge contacts on the watch body may not align with the cradle pins. Check that the rear cover clicks fully into place around its entire perimeter. Once seated correctly, the watch face should light up within five seconds of cradle contact — if it does not, rotate the watch 180° on the cradle and check again.