Nokia Lumia 640 BV-T5C Replacement Battery 3.8V 2600mAh

Nokia Lumia 640 / RM-1072 / RM-1073 — 3.8V Li-ion Replacement Battery (BV-T5C)

This is a 3.8V, 2600mAh Li-ion cell replacing the OEM BV-T5C battery in the Nokia Lumia 640 (RM-1072, RM-1073). It fits the original battery bay without modification and uses the same three-contact connector the device expects. Capacity matches the product data at 9.88Wh.

• Lumia 640 platform fit: The RM-1072 (LTE) and RM-1073 (dual-SIM) variants share the same battery bay dimensions and contact layout, so one cell covers both. The BMS negotiates with the phone's charge IC over the same protection rail used on the original pack.
• Bench tested on actual hardware: We cycled this cell through full charge and discharge on a Lumia 640 unit. The BMS held the 4.35V charge ceiling correctly and tripped undervoltage protection at 3.0V without requiring a manual reset.
• Fuel gauge recalibration on first use: After fitting this cell, disable any fast-charge mode and run one complete discharge-charge cycle at standard rate. This gives the phone's fuel gauge IC time to map the new cell's discharge curve before high-current charging begins — skipping this step is the primary cause of erratic percentage readings after a cell swap.

Sudden shutdown at 20–30% on the Lumia 640 after a cell swap

This happens when the fuel gauge IC is still calibrated to the degradation curve of the old cell. The new cell has a steeper voltage drop under modem or display load than the phone's coulomb counter expects at that state-of-charge reading. The phone interprets the voltage sag as a hard undervoltage event and cuts power. One full slow-charge cycle recalibrates the counter — after that cycle, shutdowns at 20–30% should stop. If they continue, check that the three contacts on the replacement cell seat cleanly against the phone's connector pins.

Phone feels warm near the battery during the first few charge cycles

A new Li-ion cell has higher internal impedance than a broken-in cell, so the charge IC dissipates more heat during the constant-current phase on the first few cycles. This is normal and tapers off as the cell completes its initial cycles. The warmth should stay at the back panel near the battery — heat at the top edge near the USB port points to a different issue with the charge IC itself. If back-panel warmth persists past the third full cycle, measure charging voltage at the port; it should read between 5.0V and 5.2V on a standard charger.