Nokia BL-4U Replacement Battery 3.7V 1200mAh Li-ion

Nokia 301 / 500 / 515 Series — 3.7V Li-ion Replacement Battery (BL-4U)

This is a 3.7V, 1200mAh Li-ion replacement for the Nokia BL-4U battery. It fits the Nokia 301, 301-1, 500, 515, and over 19 additional Nokia feature phone models that share the same BL-4U footprint and connector. Capacity is rated at 4.44Wh, matching the original Nokia specification.

• BL-4U platform compatibility: These Nokia models share a common 3.7V single-cell architecture, identical connector pinout, and the same BMS handshake protocol — which is why one cell revision covers all of them without modification.
• Bench tested on actual hardware: We cycled this cell on a Nokia 301 and monitored BMS cutoff at both ends of the charge curve. The protection circuit tripped correctly at the low-voltage threshold, and charge termination fired at 4.2V as expected.
• Fuel gauge recalibration on first install: After fitting this cell, run one full discharge down to auto-shutdown, then charge uninterrupted to 100% before normal use. The Nokia fuel gauge IC is calibrated to the old cell's discharge curve — one complete cycle rewrites the reference and stops erratic percentage readings.

Sudden shutdown at 20–30% on the replacement cell

The Nokia 301 fuel gauge IC stores a discharge curve from the previous cell. A new cell with a slightly different internal resistance profile hits a voltage point the IC doesn't recognise as safe — it cuts power even though charge remains. This isn't a faulty cell; it's a calibration mismatch between the new chemistry and the stored reference. Run one full discharge-to-shutdown cycle followed by a complete uninterrupted charge, and the IC rewrites its cutoff threshold to match the new cell's actual 3.0V floor.

Phone reports wrong battery percentage after cell swap

Nokia's fuel gauge IC uses a coulomb counter anchored to a learned capacity value from the original cell. Swapping cells doesn't reset that stored value, so the percentage readout drifts — it may read 50% and shut down, or read 20% with significant charge still available. The fix is the same full-cycle recalibration: discharge completely to auto-off, then charge to 100% in one session without interruption. After that cycle, the coulomb counter reanchors to the new cell's actual capacity and percentage accuracy stabilises.