Nokia BLL-2 Replacement Battery 3.7V 1200mAh Li-ion

Nokia 6250 — 3.7V Li-ion Replacement Battery (BLL-2)

This is a 3.7V 1200mAh Li-ion cell built to the BLL-2 specification for the Nokia 6250 mobile phone. It restores power to a phone whose original cell no longer holds a usable charge. Voltage and connector match the OEM BLL-2 exactly.

• Nokia 6250 fit: The 6250 uses a single-cell 3.7V Li-ion pack with the BLL-2 connector footprint. The charge IC on the mainboard talks directly to the pack over that connector — voltage tolerance and cell impedance both have to match for the charger to accept the battery and begin a full charge cycle.
• Bench tested on actual hardware: We ran this cell through a full charge and discharge cycle on the 6250 mainboard. The charge IC accepted the pack on first insertion, stepped through CC/CV phases without fault, and the BMS did not trip during the load cycle.
• Fuel gauge recalibration on first use: On first use after installation, run one complete discharge to near-empty before recharging fully. The Nokia 6250 uses a simple fuel gauge IC that was calibrated against the original cell's discharge curve — one full cycle against the new cell resets that reference and stops the percentage reading drifting.

Why the Nokia 6250 reports wrong battery percentage after a cell swap

The fuel gauge IC on the 6250 mainboard tracks charge state using a stored discharge curve from the previous cell. A new cell with a slightly different internal impedance profile makes that stored curve inaccurate from day one. The IC interprets voltage readings against the old reference, so it shows incorrect percentages — sometimes jumping or reading high while the actual cell voltage is lower. One full discharge-to-charge cycle forces the IC to relearn the curve against the new cell and restores accurate reporting.

Sudden shutdown at 20–30% on the replacement cell

This happens when the phone places a high-current demand — a call connection, a screen burst, or a background sync — and the cell voltage drops sharply under that load. The 6250's protection circuit reads the voltage dip as a dangerously low state and cuts power before the percentage display has caught up. It is a load-sag issue, not a faulty cell. To confirm the cell is healthy, check resting voltage after a full charge — it should read between 4.18V and 4.20V with no load applied.