About this replacement
Fossil Julianna HR FTW6035 — 3.8V Li-Polymer Replacement Battery (APP00296)
This 3.8V, 300mAh lithium-polymer cell is a direct replacement for the Fossil Julianna HR FTW6035 smartwatch. It fits the women's hybrid smartwatch platform that runs heart rate monitoring, fitness tracking, and notification functions. Dimensions are 28.70 × 23.60 × 3.80mm — verify against the original cell before fitting.
- Julianna HR FTW6035 fitment: The FTW6035 uses a compact Li-Polymer cell constrained by the watch's slim case profile. The APP00296 matches the original cell's footprint, connector orientation, and voltage rail so the BMS handshake proceeds without faults on power-up.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on a smartwatch test rig. The BMS accepted the new cell without entering lockout, and the fuel gauge IC initialised correctly after a full charge from near-zero following swap.
- Fuel gauge calibration after swap: Place the watch on its magnetic charger immediately after fitting the new cell. Let it charge to 100% before first use. The fuel gauge IC on the FTW6035 cannot set its reference point without a complete charge cycle from near-depletion — skipping this step causes the percentage display to read incorrectly for days.
Why the FTW6035 shows 0% immediately after a battery swap
The Julianna HR uses a fuel gauge IC that stores a learned charge reference in volatile memory. When the cell is disconnected, that reference is lost. On first power-up with a new cell, the IC has no baseline and defaults to 0% or a random low value. This is not a fault with the replacement cell. Charge the watch to 100% uninterrupted before using it — the IC resets its calibration at the top of the charge curve.
Watch not pairing to phone after battery replacement
Removing power during a battery swap terminates the active BLE session between the watch and the paired phone. The phone retains the old session token, but the watch starts fresh with no matching record. The watch will not reconnect automatically in this state. Open the Fossil app, remove the watch from paired devices, then re-pair from scratch — the new BLE handshake completes in under a minute.