Vivo B-U3 V2145 Replacement Battery 7.78V 2300mAh

Vivo X80 Pro 5G / V2145 / V2185A — 7.78V Li-Polymer Replacement Battery (B-U3)

The B-U3 is a 7.78V, 2300mAh lithium-polymer cell that fits the Vivo V2145, V2185A, and X80 Pro 5G. It replaces a degraded or failed original battery and restores power delivery to the processor, display, and cellular radio. Capacity is 17.89Wh — matched to the original cell specification.

• V2145, V2185A, and X80 Pro 5G compatibility: All three models share the same 7.78V dual-cell Li-Polymer architecture and connector pinout. The BMS handshake protocol and charge termination voltage are identical across this platform, so one cell fits all three without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the X80 Pro 5G platform. The BMS accepted charge termination at 8.72V, held low-voltage cutoff at 6.0V, and showed no thermal events across three full cycles.
• First-cycle fast charge behaviour: On first use after installation, disable fast charging for one complete discharge-charge cycle. This lets the fuel gauge IC recalibrate its coulomb counter against the new cell's discharge curve before high-current fast charging pushes elevated current into an uncalibrated cell.

Sudden shutdown at 20–30% on the X80 Pro 5G after a cell swap

A fresh B-U3 cell has a discharge curve the fuel gauge IC has never seen. The IC still references the old cell's voltage-to-capacity map, so it misreads actual state of charge. Under modem or display load, the cell voltage drops sharply at the real empty point — which the OS thinks is still 20–30%. The phone shuts down to protect the cell from going below its 6.0V cutoff. One full discharge-charge cycle corrects the coulomb counter and eliminates the premature shutdown.

USB-PD fast charge not working after replacement

Vivo's proprietary fast charge protocol requires a BMS authentication handshake before the charge IC allows high-current delivery. On the first cycle after fitting a new B-U3, the BMS may complete this handshake only at standard 5V input while it initialises. Charge the phone once to 100% using the original Vivo charger at standard rate. After that first full cycle, fast charge resumes normally on subsequent charges.