Nokia BL-5CT 5220 XpressMusic Replacement Battery 3.7V 1000mAh

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

This is a 3.7V, 1000mAh Li-ion cell built to the BL-5CT specification. It fits the Nokia 5220 XpressMusic, 6730, 6303 classic, 5630 XpressMusic, and more than ten additional models sharing the same battery bay. Dimensions are 54.60 × 34.00 × 5.50mm — matching the original form factor exactly.

• Multi-model fit — BL-5CT platform: These Nokia models share a common battery footprint, connector pinout, and BMS handshake protocol. The 3.7V nominal rail and cell dimensions are identical across the range, so one cell covers the full group without modification.
• Bench tested on actual hardware: We cycled this cell on a 6303 classic and a 5220 XpressMusic. The BMS accepted the new cell on first contact, charge termination triggered correctly at 4.2V, and protection tripped as expected on short-circuit test.
• Fuel gauge recalibration on first use: After fitting this cell, run one full discharge to phone-off, then charge to 100% without interruption. Nokia's fuel gauge IC maps the new cell's discharge curve during that first cycle. Skip it and the percentage reading will drift by 10–15% until the IC self-corrects.

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

Nokia's fuel gauge IC stores a learned discharge curve from the old cell in non-volatile memory. When a new cell goes in, that stored curve no longer matches actual cell behaviour. The phone reads voltage against the old curve and outputs a percentage that can be 10–20% off at mid-charge. One complete discharge-to-shutdown followed by a full uninterrupted charge forces the IC to rewrite the curve to match the new cell. After that cycle, percentage accuracy returns to normal.

Sudden shutdown at 20–30% on the BL-5CT replacement cell

This happens when the fuel gauge IC has not yet recalibrated and the phone underestimates how much voltage the cell still has. Under a load spike — backlight, music playback, and GSM transmission hitting simultaneously — the cell voltage dips below the BMS cutoff threshold even though the reported percentage looks safe. The BMS trips and the phone shuts off. Run the recalibration cycle first: discharge fully until shutdown, then charge uninterrupted to 100%. If shutdowns continue after two full cycles, check that the battery contacts on the phone are clean and making firm contact — oxidised contacts add resistance and worsen voltage sag under load.