Nokia N9 BV-4D Replacement Battery 3.7V 1250mAh

Nokia N9 Series — 3.7V Li-ion Replacement Battery (BV-4D)

This is a 3.7V, 1250mAh Li-ion cell built to the BV-4D spec for the Nokia N9 MeeGo smartphone. It fits the N9 16GB and 64GB variants, including the Lankku market release. Swap it in when the original cell can no longer sustain a full day of use.

• N9 16GB, 64GB, and Lankku compatibility: All N9 variants share the same 3.7V battery bay, connector pinout, and BMS communication line. One cell covers the full hardware family without modification.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on the N9 platform. The BMS handshake completed correctly, charge termination triggered at the right cutoff voltage, and the fuel gauge IC accepted the new cell without throwing a fault state.
• Fuel gauge recalibration on first use: After installation, disable fast charging if available and run one complete discharge down to auto-shutdown, then charge to 100% uninterrupted. This gives the fuel gauge IC a clean reference curve for the new cell before high-current cycles begin.

Why the N9 reports wrong battery percentage after a cell swap

The N9 uses a fuel gauge IC that tracks capacity by measuring current in and out of the cell over time — a process called coulomb counting. When you replace the cell, the IC still holds the discharge curve it learned from the old, degraded battery. That mismatch causes the percentage reading to drift, often showing 60% when the phone is close to shutdown. One full discharge-to-shutdown followed by an uninterrupted charge to 100% forces the IC to rebuild its reference curve against the new cell and re-anchor the 0% and 100% endpoints correctly.

Sudden shutdown at 20–30% on the replacement cell

This is a voltage cliff issue, not a capacity problem. Under the load of the N9's display and cellular radio, the cell voltage drops sharply below the threshold the BMS uses to protect the cell from deep discharge, and the phone cuts off before the percentage reaches zero. It happens most often in the first few cycles because the fuel gauge IC is still running on stale calibration data. After one full recalibration cycle, the IC tracks the voltage curve accurately and the shutdowns stop. If the problem continues past two full cycles, check that the replacement cell resting voltage sits above 3.6V with a multimeter before re-inserting it.