Microsoft Lumia 950 XL BV-T4D Replacement Battery 3.9V 2950mAh

Microsoft Lumia 950 XL — 3.9V Li-ion Replacement Battery (BV-T4D)

This is a 3.9V, 2950mAh Li-ion cell built to the BV-T4D specification for the Lumia 950 XL and Lumia 950 XL Dual SIM (also sold as Cityman). It replaces the original battery when the cell has degraded, won't hold a charge, or the phone refuses to power on. Voltage, dimensions, and connector match the OEM spec exactly at 80.40 × 64.00 × 4.40mm.

• Lumia 950 XL, 950 XL Dual SIM, and Cityman fit: All three share the same physical housing, connector pinout, and BMS handshake protocol. The BV-T4D spec covers the full voltage rail from 4.35V charged down to the 3.0V cutoff the phone's charge IC expects.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on a Lumia 950 XL unit. The BMS communicated correctly with the phone's fuel gauge IC and accepted both standard and Qualcomm Quick Charge cycles without tripping overcurrent cutoff.
• Fuel gauge recalibration on first use: On the first cycle after installation, disable fast charging and run one full discharge down to auto-shutdown, then charge to 100% uninterrupted. This lets the coulomb counter recalibrate against the new cell's actual discharge curve before high-current charging begins.

Sudden shutdown at 20–30% on the Lumia 950 XL after a cell swap

The Lumia 950 XL's Snapdragon 810 modem and QHD display pull current spikes that can expose a voltage cliff in a new or aged cell. When the cell voltage drops sharply under that load — even briefly — the phone's protection circuit cuts power before the displayed percentage reaches zero. This is not a faulty battery; it is the fuel gauge IC working from a discharge curve mapped to the old cell. One full uninterrupted discharge-to-shutdown followed by a full charge corrects the curve and pushes the cutoff point back down below 10%.

USB-PD fast charge not activating on the first cycle after replacement

The Lumia 950 XL negotiates USB-PD charging through the battery's BMS on the first connection. With a new cell, the BMS starts in a conservative state and may reject the higher voltage contract until it completes one standard-rate charge cycle. If fast charge shows as inactive in the battery settings screen, charge once at standard rate via a non-PD 5V adapter. On the next connection to a USB-PD charger, the BMS handshake completes and the phone should accept up to the full 3A charge rate.