About this replacement
Huawei Watch Fit PNX-B19 / Watch GT4 46mm — 3.89V Li-Polymer Replacement Battery (HB572728EGW)
This is a 3.89V, 530mAh Li-Polymer cell replacing part number HB572728EGW. It fits the Huawei Watch Fit (PNX-B19) and Watch GT4 46mm. Dimensions are 28.00 × 26.90 × 5.50mm — measure your original before fitting if unsure.
- PNX-B19 and Watch GT4 46mm compatibility: Both models share the HB572728EGW cell format, the same voltage rail, and the same flex-connector tab orientation. One cell covers both platforms without modification.
- Bench tested on actual hardware: We cycled this cell through the watch's charge IC and confirmed the BMS accepted the new cell, held the charge curve correctly, and passed the over-discharge protection threshold at the expected low-voltage cutoff.
- Post-swap fuel gauge reset: After fitting, place the watch immediately on its magnetic charger and charge fully to 100% before first use. The fuel gauge IC on this platform loses its reference point when the cell is swapped and cannot recalibrate without a complete charge cycle from near-zero.
Why continuous heart rate monitoring accelerates capacity fade on this cell
The Watch Fit's optical HR sensor fires at roughly 25Hz during continuous monitoring mode, pulling a near-constant current load on top of the display and BLE stack. A 530mAh cell is already a compact unit, so sustained sensor draw keeps the cell operating at a higher C-rate than intermittent-only use. Over time, this cycling pattern degrades capacity faster than normal daily use. If you use always-on HR, expect to recalibrate your drain expectations in the first week while the new cell settles into your usage profile.
Watch not pairing to phone after battery replacement
Removing the cell cuts power to the BLE controller and drops the active pairing session entirely. The phone retains the old device record, but the watch reinitialises with no session state — the two sides no longer agree on bonding keys. Re-pairing is required, not optional. On the phone, remove the watch from Bluetooth settings and from the Huawei Health app, then initiate a fresh pair from the watch's Bluetooth menu.