Nokia BL-4UL Asha 225 Replacement Battery 3.7V 1200mAh

Nokia Asha 225 / New 3310 — 3.7V Li-ion Replacement Battery (BL-4UL / BL-4WL)

This 3.7V Li-ion cell replaces the OEM BL-4UL and BL-4WL batteries in the Nokia Asha 225 (RM-1012) and the Nokia New 3310 (2017 revision). Capacity is 1200mAh (4.44Wh), matching the original spec. Both models share the same battery footprint, connector pinout, and BMS handshake requirements, so one cell covers the full compatibility range listed above.

• Asha 225 and New 3310 platform fit: These models share a common battery bay dimension (60.60 × 38.00 × 4.50mm), identical three-pin connector, and the same fuel gauge IC communication protocol. A single cell revision covers all listed variants without modification.
• Bench tested on actual hardware: We cycled this cell through the Nokia charge IC handshake on a 3310 (2017). The BMS accepted the constant-current phase correctly, terminated at the expected 4.2V cutoff, and did not trigger any overtemperature flags during the first three cycles.
• Fuel gauge recalibration on first use: On the Nokia 3310 and Asha 225, the onboard fuel gauge IC carries the calibration curve from the old cell. After fitting this replacement, run one complete discharge down to auto-shutdown and a full uninterrupted charge before relying on the percentage readout — this resets the coulomb counter against the new cell's actual discharge curve.

Why the Nokia 3310 (2017) reports wrong battery percentage after a cell swap

The 3310's fuel gauge IC stores a learned discharge curve from the original cell. When you fit a new cell, that stored curve no longer matches the actual voltage-to-capacity relationship of the fresh Li-ion. The percentage readout stays anchored to the old model until the IC observes a full discharge-charge cycle on the new cell. One complete cycle — from auto-shutdown to 4.2V charge termination — is enough for the coulomb counter to rebuild an accurate state-of-charge map. Until that cycle completes, readings above 80% and below 30% are particularly unreliable.

Sudden shutdown at 20–30% on the Asha 225 after replacement

This happens when the cell voltage drops sharply under load — screen backlight, active call, or keypad polling — before the fuel gauge IC predicts empty. A fresh Li-ion cell has a steeper voltage cliff than an aged cell, so the phone's low-voltage cutoff trips while the percentage still reads mid-range. The fix is the same calibration cycle: one full discharge to auto-shutdown, then charge to 4.2V without interruption. If shutdowns continue after two full cycles, check that the battery contacts on the phone chassis are clean and making firm contact — a high-resistance connection causes a voltage drop that mimics a depleted cell.