About this replacement
Vivo S7e 5G 2020 — 3.87V Li-Polymer Replacement Battery (B-P7)
This is a 3.87V, 4000mAh (15.48Wh) Li-Polymer replacement battery for the Vivo S7e, S7e 5G 2020, V2031EA, and V2031. It carries OEM part number B-P7 and restores normal operation in phones where the original cell has degraded through repeated charge cycles or extended storage.
- S7e / V2031 series compatibility: These models share the same battery bay geometry, connector pinout, and BMS handshake protocol. The B-P7 designation is consistent across V2031EA and V2031 variants, meaning the same cell, same NTC thermistor wiring, and same charge IC communication lines apply to all four models listed.
- Bench tested on actual hardware: We ran this cell through a full charge-discharge cycle on the S7e platform. The BMS accepted the charge IC handshake on the first cycle, NTC readings stayed within normal range throughout, and the coulomb counter initialised without fault flags in the system log.
- Fuel gauge recalibration on first use: After fitting this cell, disable fast charging and complete one full discharge-charge cycle at standard rate. This lets the fuel gauge IC map its reference curve against the new cell before high-current charging is applied to an uncalibrated coulomb counter.
Sudden shutdown at 20–30% on the S7e after a cell swap
This happens because the fuel gauge IC is still referencing the discharge curve of the old, degraded cell. When the new cell's actual voltage drops under modem or display load, it hits a voltage cliff the gauge wasn't expecting. The phone interprets the sag as a critical low-voltage condition and cuts power to protect the SoC. One full discharge-charge cycle at standard rate forces the coulomb counter to rebuild its reference map against the new cell's actual discharge profile, and the shutdowns stop.
USB-PD fast charge rejected on the first cycle after replacement
On the first charge after fitting a new cell, the BMS may not complete the handshake with the phone's charge IC fast enough for the USB-PD negotiation to succeed. The charger falls back to standard 5V charging as a safe default. This is not a fault with the cell or the charger — the BMS initialises its internal registers on the first cycle and the fast charge protocol is accepted from the second cycle onward. Plug in, let it charge at standard rate, unplug fully, then reconnect to confirm fast charge resumes at the expected wattage.