About this replacement
Vivo X50 Pro / X51 5G — 3.87V Li-Polymer Replacement Battery (B-N3)
The B-N3 is the OEM-matched Li-Polymer cell for the Vivo X50 Pro, X50 Pro 5G, X51 5G, and V2005. It runs at 3.87V with a 4200mAh (16.25Wh) capacity — the same electrical spec as the original cell. Fits the standard connector and sits within the original battery bay dimensions of 76.70 × 62.45 × 4.60mm.
- X50 Pro and X51 5G platform compatibility: Both devices share the same battery bay dimensions, voltage rail, and BMS handshake protocol, which is why a single B-N3 cell covers the full lineup. The connector pinout and charge IC communication are identical across V2005 and the 5G variants.
- Bench tested on actual hardware: We cycled this cell through full charge and discharge on an X50 Pro unit. The BMS accepted the cell without error flags, charge IC communication stayed stable throughout, and voltage held steady under screen and modem load.
- Fuel gauge recalibration on first cycle: On first use after installation, disable fast charging for one complete discharge-charge cycle. This lets the fuel gauge IC map its coulomb counter to the new cell's discharge curve before high-current charging pushes current into an uncalibrated state.
Sudden shutdown at 20–30% on the X50 Pro after a cell swap
A new cell has a slightly different voltage-versus-capacity curve than the worn cell the fuel gauge IC was calibrated against. When the phone hits the old cell's low-voltage cliff — around 3.5V under modem or display load — the BMS cuts power even though usable capacity remains. The fuel gauge reports 20–30% because it's reading a curve that no longer matches the new cell. One full slow discharge to shutdown followed by a complete charge to 100% resets the coulomb counter to the correct curve.
USB-PD fast charge not activating on the first cycle after replacement
The X50 Pro's charge IC uses a handshake with the BMS to confirm cell state before enabling high-current fast charge. On a freshly installed cell with no charge history, the BMS reports an unknown state and the charge IC defaults to standard 5V input as a protection measure. This is not a fault — it clears after the first complete charge cycle. Connect to the original Vivo charger, let it complete a full charge to 100%, and fast charge will activate from the second cycle onward.