Nokia N75 BL-5BT Replacement Battery 3.7V 800mAh

Nokia N75 / 2600 Classic / 7510 Supernova — 3.7V Li-ion Replacement Battery (BL-5BT)

This is a 3.7V, 800mAh Li-ion replacement for the Nokia BL-5BT cell. It fits the N75, 7510, 2600 classic, and 7510 Supernova handsets. Swap it when the original cell no longer holds a charge or shuts the phone down unexpectedly.

• N75, 2600 classic, and 7510 platform fit: These models share the same BL-5BT footprint, connector polarity, and 3.7V nominal voltage rail. The BMS handshake on each device accepts the same cell chemistry, so one replacement covers all four models without modification.
• Bench tested on actual hardware: We cycled this cell on the N75 and 2600 classic. The BMS accepted the new cell on first insertion, charge termination triggered cleanly at full voltage, and no thermal events occurred during the charge cycle.
• Fuel gauge recalibration on first use: After installing this cell, disable fast charging for the first full discharge-charge cycle. This gives the fuel gauge IC time to map the new cell's discharge curve before high-current charging begins — preventing erratic percentage readings from the start.

Why the N75 reports wrong battery percentage after a cell swap

The N75 uses a fuel gauge IC that builds its capacity model from accumulated discharge data on the original cell. When you install a new cell, that learned curve no longer matches the actual chemistry. The IC reports percentage based on the old model, so the number shown is wrong — not the cell. One complete discharge down to automatic shutdown, followed by a full charge to 4.2V, resets the coulomb counter to the new cell's actual capacity curve.

Sudden shutdown at 20–30% on the replacement cell

This happens when the cell voltage drops sharply under load — a classic voltage cliff on a cell the fuel gauge IC hasn't calibrated yet. The modem radio or screen backlight draws a current spike the uncalibrated gauge didn't predict, and the BMS cuts power before the displayed percentage reaches zero. It is not a faulty cell. Run one full discharge-charge cycle and confirm the cell reaches 4.2V at the top of charge — the shutdowns stop once the gauge IC has a calibrated curve to work from.