Vivo T1x B-R3 Replacement Battery 3.87V 4900mAh

Vivo T1x / V2123A — 3.87V Li-Polymer Replacement Battery (B-R3)

The B-R3 is a 4900mAh Li-Polymer cell at 3.87V, built to replace the original battery in the Vivo T1x, T1x 5G 2021, and V2123A. Capacity loss in these phones typically shows up as sudden shutdowns or a screen that barely lasts through a day. This cell restores the original charge reservoir at the same physical footprint — 93.20 × 62.70 × 4.50mm.

• T1x / V2123A platform fit: The T1x and V2123A share the same battery bay geometry, connector pinout, and BMS handshake protocol. One cell covers all three listed variants without modification.
• Bench tested on actual hardware: We ran the B-R3 through full charge and discharge cycles on V2123A units. The BMS accepted the cell on first connection, protection circuits triggered correctly at low-voltage cutoff, and the charge IC stepped through CC/CV phases without fault flags.
• Fuel gauge recalibration after install: On first use after installation, disable fast charging and run one complete discharge-charge cycle at standard rate. This lets the fuel gauge IC map the new cell's discharge curve before fast charging pushes high current into an uncalibrated cell — otherwise percentage readouts will drift.

Sudden shutdown at 20–30% on the Vivo T1x after a cell swap

A new cell has a slightly different internal resistance profile than the original. Under modem load or a screen-on burst, the phone draws enough current to pull cell voltage below the BMS cutoff threshold — even though the fuel gauge still reads 20–30%. The fuel gauge IC has not yet recalibrated its coulomb counter to the new cell, so the percentage shown does not match actual cell state. Run one full discharge to auto-off, then charge uninterrupted to 100% at standard rate. After that cycle, the coulomb counter resets to the new cell curve and the shutdowns stop.

USB-PD or fast charge not activating after replacement

On first connection, some Vivo charge ICs run a brief BMS handshake before enabling fast-charge current. If the cell voltage sits below a set threshold after storage, the IC stays in trickle mode and fast charge never kicks in. Plug the phone in for 10–15 minutes on a standard 5V charger first, letting the cell voltage climb above 3.5V per cell. Once that floor is reached, disconnect and reconnect the fast charger — the handshake completes and full charging current resumes.