Microsoft Lumia 640 XL 3.8V 3000mAh Replacement Battery

Microsoft Lumia 640 XL — 3.8V Li-Polymer Replacement Battery

This 3.8V, 3000mAh Li-Polymer cell is a direct swap for the battery in the Microsoft Lumia 640 XL, covering variants RM-1062 and RM-1063. It delivers 11.4Wh of capacity to power the Snapdragon 400 SoC, 5.7-inch display, and LTE modem. Physical dimensions are 100.91 × 46.90 × 4.75 mm — fitting the original battery bay without modification.

• RM-1062 and RM-1063 compatibility: Both Lumia 640 XL variants use the same battery bay dimensions, connector pinout, and charge IC handshake. One cell covers both hardware revisions without adapters or modifications.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on a Lumia 640 XL unit. The BMS accepted charging from the standard charger without triggering overcurrent cutoff, and the fuel gauge IC read capacity within normal variation across three full cycles.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging and run one complete discharge-charge cycle at standard rate. This allows the fuel gauge IC to map the new cell's discharge curve before high-current charging begins pushing load into an uncalibrated state.

Sudden shutdown at 20–30% on the Lumia 640 XL

This is a voltage-cliff failure, not a capacity failure. Under peak load — LTE modem active, screen at full brightness — the cell voltage drops below the BMS cutoff threshold faster than the fuel gauge IC can report. The phone shuts off because actual cell voltage hits the floor while the percentage counter still shows charge remaining. Running one full discharge-charge cycle recalibrates the coulomb counter and reduces the gap between reported and actual state of charge. If shutdowns persist past two calibration cycles, check that the cell connector is fully seated.

Phone not powering on after the replacement cell sat in storage

Li-Polymer cells self-discharge in storage. If this battery was stored discharged, the BMS may have entered lockout below 2.5V per cell to prevent damage. The phone will not respond to a normal boot attempt in this state. Connect it to a charger and leave it for 20–30 minutes before pressing the power button — the charge IC needs time to trickle-charge the cell above the BMS re-initialisation threshold. If the device still does not respond, verify the charger is delivering at least 5V 1A and check the USB port for debris.