Vivo T2x Replacement Battery B-U2 3.87V 5900mAh

Vivo T2x / V2188A — 3.87V Li-Polymer Replacement Battery (B-U2)

This is a 3.87V, 5900mAh Li-Polymer cell for the Vivo T2x and V2188A smartphones. It replaces part number B-U2, the original cell used across both model variants. Dimensions are 94.10 × 63.80 × 5.30mm — measure your existing cell before fitting.

• T2x and V2188A compatibility: Both models run the same B-U2 cell with identical voltage rails, connector pinout, and BMS handshake protocol — one cell covers both variants without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the T2x platform. The BMS accepted the cell, charge current stepped correctly through CC and CV phases, and protection circuits tripped at expected cutoff thresholds.
• 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 fast charging pushes current into an uncalibrated cell.

Sudden shutdown at 20–30% on the T2x after a cell swap

The T2x fuel gauge IC holds a discharge curve calibrated to the original cell. A new cell with a slightly different internal resistance profile can hit a voltage cliff under modem or display load before the gauge reads zero. The phone interprets the voltage drop as an immediate low-power condition and shuts down. One full discharge-charge cycle without fast charging resets the coulomb counter and maps the new curve. After that cycle, the percentage reading stabilises and shutdowns stop.

USB fast charge not activating after replacement on the T2x

On the first charge cycle with a new cell, the charge IC may withhold fast-charge handshake until the BMS reports a valid state-of-charge above a minimum threshold — typically around 10–15%. Plugging in below that threshold often locks the port to standard 5V charging only. Let the phone charge at standard rate until it crosses that threshold, then disconnect and reconnect the cable. Fast charging should engage at that point and continue normally on subsequent cycles.