Fossil Kate Spade DW9P1 Smartwatch Replacement Battery 3.8V 350mAh

Fossil Kate Spade DW9P1 / DW9K1 — 3.8V Li-Polymer Replacement Battery (APP00286)

This is a 3.8V, 350mAh lithium-polymer cell replacing part number APP00286 in the Kate Spade DW9P1 and DW9K1 smartwatches. Both watches share the same battery bay geometry (28.00 × 23.50 × 4.20mm) and BMS handshake, so one part covers both references. Capacity matches the original spec exactly — no guesswork on fit or connector polarity.

• DW9P1 and DW9K1 platform compatibility: These two Kate Spade models share the same mainboard revision and fuel gauge IC. The connector pinout, physical footprint, and BMS communication protocol are identical across both, so APP00286 is the correct cell for either watch without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on a DW9P1 mainboard and confirmed the BMS accepted the cell without throwing a fault code. Charge acceptance reached full capacity within the first cycle, and the fuel gauge reported correctly after calibration.
• Post-swap charge cycle on Kate Spade watches: After fitting this cell, place the watch on its magnetic charger immediately and charge to 100% before use. The fuel gauge IC on this platform loses its reference point when the original cell is removed — it cannot calibrate accurately without a full charge from near-zero after a swap.

Why the DW9P1 shows incorrect battery percentage after a cell swap

The DW9P1 uses a coulomb-counting fuel gauge IC that tracks charge state relative to a stored baseline. When the original cell is removed, that baseline is wiped. The IC then reads the new cell's open-circuit voltage and makes a rough estimate — often wildly inaccurate. A full charge cycle from near-zero resets the baseline and restores accurate percentage reporting. Until that cycle completes, readings of 0%, 100%, or random jumps are all expected behaviour, not a faulty cell.

Watch not pairing to the app after battery replacement

Removing power kills the active Bluetooth Low Energy session between the DW9P1 and the paired phone. The watch does not automatically re-establish that session on reboot — the phone treats it as a disconnected device. Go to the phone's Bluetooth settings, forget the watch, then re-pair through the Kate Spade Connected app from scratch. Do not attempt to re-pair without first forgetting the old pairing entry — that step is skipped most often and causes the re-pair to fail.