About this replacement
Asus ZenWatch 2 WI501QF Series — 3.8V Li-Polymer Replacement Battery (C11N1540)
This 3.8V, 360mAh Li-Polymer cell replaces the original C11N1540 battery in the Asus ZenWatch 2 WI501QF, WI501Q, and WI501QF. It restores power to the watch's display, notifications, heart rate monitoring, and Bluetooth connectivity. Dimensions are 38.23 × 25.24 × 3.90mm — confirm these against your existing cell before fitting.
- ZenWatch 2 WI501Q and WI501QF compatibility: Both models run the same 3.8V power rail with the same flex connector and BMS handshake, so one cell covers the full WI501Q lineup. The OEM part numbers C11N1540 and 0B200-01630100 refer to the same physical cell.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on the ZenWatch 2 platform. The BMS accepted the new cell without faults, and the fuel gauge IC registered voltage correctly after a full charge cycle from near-zero.
- Post-swap charging on the ZenWatch 2: After fitting, place the watch on its magnetic charger immediately and charge to 100% before first use. The fuel gauge IC on this platform loses its reference point when the cell is swapped — it cannot re-calibrate without a full charge cycle starting from near-zero. Skipping this step causes the percentage readout to behave erratically for days.
Why the ZenWatch 2 charge percentage jumps or reads wrong after a cell swap
The ZenWatch 2 uses a coulomb-counting fuel gauge IC that tracks charge state relative to a stored reference. Removing the old cell wipes that reference entirely. When you fit a new cell and power on without completing a full charge cycle first, the IC is estimating from a blank slate and will display incorrect percentages — sometimes jumping from 80% to 20% mid-use. A single full charge from near-zero resets the reference and stabilises the readout within one to two cycles.
Watch not pairing to phone after battery replacement
Removing power during a battery swap terminates the active Bluetooth Low Energy session between the watch and the paired phone. The watch comes back up with a new session ID, and the phone's Bluetooth stack still expects the old one. On the phone, go to Bluetooth settings, forget the ZenWatch 2 entirely, then re-pair from scratch through the Asus ZenWatch app. Do not attempt to reconnect from the Bluetooth quick-settings panel — use the app's pairing flow to rebuild the full connection profile.