Vivo S7 5G Replacement Battery B-N8 3.87V 3700mAh

Vivo S7 5G / V20 Pro 5G — 3.87V Li-Polymer Replacement Battery (B-N8)

This is a 3700mAh Li-Polymer cell rated at 3.87V nominal, built to the B-N8 specification. It fits the Vivo S7 5G, V20 Pro 5G, V2020A, and V2020CA. Install it when the original cell can no longer hold a full charge or causes unexpected shutdowns.

• S7 5G and V20 Pro 5G platform fit: These models share the same battery bay geometry, connector pinout, and BMS handshake protocol. The B-N8 cell communicates directly with the fuel gauge IC on both boards without requiring any hardware modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the S7 5G mainboard. The BMS accepted the cell on first connection, charge current ramped normally through CC/CV stages, and the protection circuit responded correctly to over-discharge cutoff.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging for one complete discharge-charge cycle. This lets the fuel gauge IC map the new cell's discharge curve before high-current charging begins on an uncalibrated cell — prevents early percentage drift and erratic readings.

Why the Vivo S7 5G shuts down suddenly at 20–30% after a battery swap

A new cell has a slightly different internal resistance profile than the degraded one it replaced. The fuel gauge IC still holds the old discharge curve in its coulomb counter, so it reports 25% remaining while the actual cell voltage is already near the low-load cliff. Under modem or display load, voltage drops sharply, hits the hardware cutoff threshold, and the phone shuts off. One full discharge-charge cycle without fast charging forces the fuel gauge IC to relearn the new curve. After that cycle, percentage readings stabilise and the premature shutdown stops.

USB-PD or Vivo fast charge not triggering on the first cycle after replacement

After fitting a new B-N8 cell, some users see the phone fall back to standard 5W charging even when using the original fast charger. This happens because the charge IC runs a brief handshake with the BMS on every new cell connection, and on the first cycle it defaults to slow charge as a precaution until cell parameters are confirmed. Disconnect the charger, reboot the phone, then reconnect. If fast charge still does not trigger, complete one full slow charge cycle — the charge IC will accept the higher current protocol on the next session once the BMS handshake completes successfully.