BV-T4D Microsoft Lumia 950 XL Replacement Battery 3.85V 3350mAh

Microsoft Lumia 950 XL / Cityman — 3.85V Li-ion Replacement Battery (BV-T4D)

This is a 3350mAh, 3.85V Li-ion cell built to the BV-T4D specification. It fits the Lumia 950 XL, Lumia 950 XL Dual SIM, and the Cityman prototype variant. Install it when the original cell no longer holds enough charge to get through a normal day.

• 950 XL and Dual SIM compatibility: Both the single and Dual SIM variants share the same battery bay dimensions and connector pinout. The BV-T4D form factor — 81.10 × 64.30 × 4.60 mm — seats correctly in either chassis without modification.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on a Lumia 950 XL unit. The BMS accepted charge current normally, and the protection circuit tripped correctly at low-voltage cutoff without requiring a manual reset.
• Fuel gauge recalibration on first use: After fitting this cell, disable fast charging for one full discharge-charge cycle. The Lumia 950 XL's fuel gauge IC calibrates its coulomb counter against the discharge curve — letting it complete one uninterrupted cycle at standard current gives it accurate data before high-current charging begins.

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

This happens because the fuel gauge IC still holds the discharge curve of the old, degraded cell. When the new cell hits a voltage point the IC associates with empty on the old curve, it signals shutdown — even though actual capacity remains. The modem and QHD display pull sharp current spikes that accelerate this voltage drop. One full discharge to auto-off followed by an uninterrupted charge to 100% resets the coulomb counter and the shutdowns stop.

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

The Lumia 950 XL negotiates fast charge via the charge IC talking to the BMS. On a new cell, the BMS starts in a cautious state and may reject the elevated current request during the first handshake. The device falls back to standard 5V charging. Completing one full charge cycle at standard current allows the BMS to confirm cell health, after which the charge IC re-negotiates the higher voltage and fast charging resumes normally.