Nokia BL-5CT 5220 XpressMusic Replacement Battery 3.7V 1200mAh

Nokia 5220 XpressMusic / 6303 classic / 6730 — 3.7V Li-ion Replacement Battery (BL-5CT)

This is a 3.7V, 1200mAh Li-ion replacement for the Nokia BL-5CT battery. It fits the Nokia 5220 XpressMusic, 6730, 6303 classic, and 5630 XpressMusic, among other models that share the same BL-5CT footprint. Dimensions are 54.60 × 34.00 × 5.50mm — verify against your existing cell before ordering.

• BL-5CT platform compatibility: Nokia spread the BL-5CT across several mid-range handsets from the same era because they share an identical voltage rail, connector pinout, and physical envelope. The 5220, 6303, 6730, and 5630 all draw from the same 3.7V single-cell architecture, so one cell fits the full group without modification.
• Bench tested on actual hardware: We ran this cell on the Nokia 5220 XpressMusic and monitored BMS handshake at power-on. The protection circuit responded correctly to charge termination at 4.2V and tripped cutoff under a simulated deep-drain condition below 2.75V per cell — no anomalous heat or voltage drop observed during the test cycle.
• Fuel gauge recalibration on first use: After fitting this cell, disable any fast-charge adapter for the first full discharge-to-charge cycle. The handset's fuel gauge IC is still calibrated to the old cell's discharge curve. Running one slow cycle at standard current lets the coulomb counter map the new cell before the charge IC applies higher current on subsequent charges.

Why the 5220 XpressMusic reports wrong battery percentage after a cell swap

Nokia's fuel gauge IC builds its percentage model from the discharge curve of the original cell over hundreds of cycles. When you fit a fresh BL-5CT replacement, the IC is still referencing the degraded curve it learned from the old battery. The new cell holds a steeper, healthier voltage curve, so the IC misreads state-of-charge and can display anywhere from 10–20% off actual capacity. One complete slow discharge down to auto-shutdown followed by a full charge to 4.2V resets the coulomb counter's reference baseline.

Sudden shutdown at 20–30% on the replacement cell

This is a voltage cliff failure, not a capacity problem. Under modem transmit load or screen brightness spikes, the phone draws a current burst that briefly drops cell voltage below the BMS cutoff threshold — even when the fuel gauge still shows charge remaining. The old fuel gauge curve makes the phone think it has reserve when the cell voltage is already near 3.4V under load. Charge the phone to 100%, then check that your charger output holds steady at 5V — a weak adapter accelerates the sag that triggers this cutoff.