About this replacement
Huawei Band B6 / Band B7 — 3.87V Li-Polymer Replacement Battery (HB431622EFW)
This is a 3.87V, 100mAh Li-Polymer cell replacing part number HB431622EFW. It fits the Huawei Band B6, Band B7, FDS-B19, and FDS-B49 fitness trackers. The cell measures 20.40 x 14.50 x 4.00mm and drops into the original battery bay without modification.
- Band B6, B7, FDS-B19, FDS-B49 compatibility: All four models share the same 3.87V cell footprint, connector pinout, and BMS handshake protocol — one cell covers the full platform range.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on the Band B6 platform. The BMS accepted the cell without error flags, and fuel gauge readout tracked correctly across the full state-of-charge window.
- First-charge calibration after swap: Place the watch on its magnetic charger immediately after fitting the new cell and charge to 100% before use. The fuel gauge IC on this platform loses its reference voltage during cell removal — it cannot calibrate the state-of-charge curve without one complete charge cycle from near-zero.
Why the Band B6 reads 0% and won't power on after a cell swap
The Band B6 uses a coulomb-counting fuel gauge IC that stores its reference data in volatile memory. When the old cell is removed, that reference is wiped. The IC has no baseline to count from, so it defaults to 0% and the BMS holds the output rail low as a protection state. This is not a faulty cell — it is the expected behaviour after any cell swap on this platform. Connect the watch to its charger, let it charge uninterrupted to 100%, and the fuel gauge will re-establish its reference at 4.35V full charge.
Charge contacts not connecting on the magnetic charger after reassembly
The Band B6 charges through exposed pogo-pin contacts on the rear housing. If the back cover shifts even slightly during reassembly, the contact pads misalign with the charger's magnetic dock and no current flows. The watch will show no charging indicator and the screen stays dark. Remove the watch from the charger, re-seat the back cover flush, and reattach — confirm you feel the magnetic snap and see the charging icon within five seconds of docking.