About this replacement
Fossil Launches LTE — 3.8V Li-Polymer Replacement Battery (APP00277)
This 3.8V, 300mAh Li-Polymer cell replaces the original battery in the Fossil Launches LTE smartwatch. It restores power to the display, processor, BLE radio, heart rate sensor, and LTE modem. Dimensions are 28.80 × 23.70 × 3.80mm — match these before fitting.
- Launches LTE platform fit: The Launches LTE draws across multiple subsystems simultaneously — LTE modem, optical HR sensor, and Wear OS processor share a single cell. This cell matches the voltage rail and connector footprint that platform requires.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on the Launches LTE platform. The BMS accepted the cell without fault flags, and the fuel gauge IC registered charge state correctly after a full initial cycle from near-zero.
- Fuel gauge recalibration after swap: Place the watch on its charger immediately after fitting this cell and charge to 100% before use. The fuel gauge IC on Wear OS platforms cannot set an accurate reference point without one full charge cycle from near-zero following a cell change.
LTE modem current spikes and what they do to a small cell
The LTE radio in the Launches LTE pulls short, sharp current spikes when it registers on a network or syncs data — more than the HR sensor or display draw individually. A worn original cell sags in voltage during these spikes, triggering low-voltage shutoff before the display reads empty. A fresh 300mAh cell at full specification handles these transient loads without the same voltage sag. If you still see unexpected shutoffs after fitting this cell, check that LTE is not set to continuous background sync.
Watch not pairing with phone after battery replacement
Removing the original cell clears the active BLE session between the watch and its paired phone. The phone retains the old pairing record, but the watch boots with no matching session — so the connection never re-establishes on its own. Open the Fossil app on your phone, remove the existing watch entry, then run a fresh pair from the watch's Bluetooth settings. Once paired, the watch reconnects to Google account sync and notification relay normally.