BL-4YW Microsoft Lumia 925 Replacement Battery 3.7V 2000mAh

Microsoft Lumia 925 Series — 3.7V Li-ion Replacement Battery (BL-4YW)

This is a 3.7V 2000mAh Li-ion cell for the Microsoft Lumia 925, 925T, and 925.2. It replaces the original BL-4YW when capacity has degraded and the phone can no longer hold charge through a normal day. Dimensions are 61.95 × 56.75 × 4.80mm — verify your tray clearance before fitting.

• Lumia 925, 925T, and 925.2 fitment: All three variants share the same battery bay dimensions, BL-4YW connector pinout, and charge IC handshake. One cell covers the full 925 line without modification.
• Bench tested on actual hardware: We cycled this cell through the Lumia 925 charge IC and confirmed the BMS accepted the charge handshake cleanly. No charge interrupt errors and no false temperature fault triggers on the first three cycles.
• First-cycle fuel gauge reset: After fitting, run one full discharge to auto-shutdown and then charge uninterrupted to 100% before normal use. The Lumia's coulomb counter is still calibrated to your old cell's discharge curve — this single cycle resets it against the new cell and stops percentage jumping.

Sudden shutdown at 20–30% on the Lumia 925 after a cell swap

This happens because the fuel gauge IC is still reading the discharge curve of the old, worn cell. A new cell has a steeper voltage cliff at low state-of-charge, so the phone's modem or screen draws enough current to drop voltage below the BMS cutoff threshold before the percentage counter reaches zero. The fix is one complete discharge-charge cycle with no interruption — this lets the coulomb counter map the new cell's actual voltage-to-capacity curve. After that cycle, shutdowns at 20–30% stop for the vast majority of units.

Phone won't power on after the replacement cell sat in storage

Li-ion cells self-discharge during storage. If the cell voltage has dropped below 2.5V, the BMS enters lockout mode and blocks current flow to protect the cell from damage. The phone will not respond to the power button and may show nothing on screen even when plugged in. Connect to a USB charger and leave it for 20–30 minutes without pressing anything — the charge IC will trickle current into the cell until voltage climbs above 2.8V, at which point the BMS releases lockout and normal charging resumes.