Vivo BA58 Replacement Battery 3.91V 6250mAh Li-Polymer I2221

Vivo iQOO Neo 10R / I2221 — 3.91V Li-Polymer Replacement Battery (BA58)

This is a 3.91V, 6250mAh Li-Polymer replacement battery carrying OEM part number BA58. It fits the Vivo I2221, iQOO Neo 10R 5G, and iQOO Neo10 R smartphones. These three model designations share the same physical cell format, connector pinout, and BMS communication protocol.

• I2221 / iQOO Neo 10R platform fit: The I2221 and iQOO Neo 10R 5G are regional variants of the same hardware platform. They run the same voltage rail, use the same five-pin flex connector, and speak the same BMS handshake — so one cell covers all three model strings without modification.
• Bench tested on actual hardware: We cycled the BA58 cell through charge and discharge on the iQOO Neo 10R 5G platform. The BMS accepted the cell on first connection, thermal reporting stayed within normal range, and the charge IC stepped through trickle, CC, and CV phases without interruption.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging and run one complete discharge-charge cycle at standard current. This lets the fuel gauge IC map the new cell's discharge curve before high-current fast charging pushes energy into an uncalibrated coulomb counter.

Sudden shutdown at 20–30% on the BA58 after replacement

This is a voltage-cliff failure, not a capacity problem. The fuel gauge IC still holds calibration data from the old cell, so it misjudges the new cell's discharge curve and calls remaining charge incorrectly. Under modem or display load, the cell voltage drops below the BMS cutoff threshold before the OS percentage reaches zero. Run one full discharge to automatic shutdown, then charge uninterrupted to 100% — after that single cycle, the coulomb counter resets against the real curve and shutdowns stop.

USB-PD or proprietary fast charge not working on first cycle after swap

Vivo's fast-charge protocol requires a BMS handshake before the charge IC steps up current. On the first cycle after a cell swap, the BMS may not complete that handshake immediately — the phone falls back to standard 5V charging instead. This is not a fault with the replacement cell. Charge to 100% at standard rate, disconnect, then reconnect — the handshake completes on the second session and fast charge resumes at rated current.