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Motorola Moto 360 2nd Compatible Battery FW3S 3.8V 250mAh

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Fits Motorola Moto 360 2nd generation smartwatch; replaces OEM part number FW3S.
3.8V, 250mAh Li-Polymer cell delivers enough capacity for full-day operation on this form-factor device.
Connector mates directly to the internal charging pads; no external connector or locking tabs present.
We ran charge cycles on a test unit; the BMS accepted the cell without fault codes or early cutoff behavior.
After installation, place the watch on its charger and run a complete charge to 100% before wearing — the fuel gauge IC cannot calibrate without a full cycle from near-empty.
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Battery Care Tips

🔹 Getting Started

Charge your new battery fully before you use it for the first time. Over the next few charge cycles, run your device down to around 20% before you recharge—this helps the battery perform its best. After that, charge whenever you need to.

🔹 Keep It Healthy

Avoid letting your battery completely drain or staying plugged in constantly. Both extremes wear it out faster. Store the battery in a cool, dry place when you're not using it, since heat damages batteries quickly.

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⚠️ Disclaimer: All product names, trademarks, and registered trademarks belong to their respective owners.

🔹 We use these names, brands, or model numbers only for identification and compatibility purposes.

Voltage

3.8V

Amp

250mAh

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.

Compatible Models

Moto 360 2nd Moto 360 2rd

Replaces Part Numbers

FW3S

Technical Specifications

Voltage3.8V
Amp Hours250mAh
Capacity250mAh
Rate0.95Wh
Net Weight4.6g /0.16 oz
Gross Weight104.6g /3.69 oz
Approximate Weight104.6g /3.69 oz
Dimension 27.30 x 25.70 x 3.75mm

Product Highlights

  • Brand: Motorola
  • Manufacturer: CS
  • Series: Standard
  • Color: Black
  • Product Type: Li-Polymer
  • Battery Type: Li-Polymer
  • Warranty: 12 Months
  • Bulk Orders: sales@batteryweb.com

Frequently Asked Questions

My Moto 360 2nd Gen died overnight after I put in the new battery — why is it draining so fast?

Always-on display mode combined with continuous heart rate monitoring pulls roughly 30–40mA sustained on this platform, which will drain a 250mAh cell faster than expected if those features are both active. Check Wear OS display settings and confirm always-on is off for the first few days after a swap. The fuel gauge also needs one full charge cycle to recalibrate after a cell replacement — inaccurate readings can cause the watch to shut down early while charge remains. Disable always-on display, complete a full charge to 100%, then reassess drain.

The heart rate sensor seems to kill this new battery faster than it did the old one — is something wrong?

This is normal for the first week after a cell swap. The heart rate sensor's LED current draw is constant, but the new cell's internal impedance is slightly higher out of the box than a broken-in cell — the BMS compensates by pulling voltage down faster under sensor load. Impedance settles after 3–5 full charge cycles, and battery life typically stabilises after that point. Run five complete charge and discharge cycles before drawing any conclusions about drain rate.

The magnetic charger shows a charge indicator but the watch stays at 0% and won't boot — what's the fix?

The charge contacts on the Moto 360 2nd Gen are spring-loaded pins that can shift out of alignment during reassembly. If the back cover is even slightly off-centre, the pins make intermittent contact — enough to light the charge LED on the cradle but not enough to deliver sustained current to the cell. Remove the watch from the charger, reseat it carefully so the flat of the charger aligns with the flat on the watch case, and confirm you hear or feel the magnetic snap. Leave it on charge for at least 30 minutes before attempting a boot.

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