Nokia BL-4CT 5310 Replacement Battery 3.7V 820mAh

Nokia 5310 / 7210 Supernova Series — 3.7V Li-ion Replacement Battery (BL-4CT)

This is a 3.7V, 820mAh Li-ion replacement battery for the Nokia BL-4CT cell. It fits the Nokia 5310, 6600 Fold, 7210 Supernova, 7310 Supernova, and eight additional models sharing the same form factor. Dimensions are 54.26 × 33.67 × 4.23mm — same as the original cell.

• Multi-model fit across the BL-4CT platform: The 5310, 7210 Supernova, 7310 Supernova, and 6600 Fold all run the same 3.7V single-cell architecture with an identical connector footprint and BMS handshake. One cell covers the full lineup because Nokia standardised the protection circuit interface across these handsets.
• Bench tested on actual hardware: We cycled this cell on a 5310 and 7210 Supernova unit. The BMS accepted charge without a protection trip, voltage held within 50mV of rated at mid-discharge, and the fuel gauge IC accepted the new cell on the first full cycle.
• First-cycle fuel gauge reset on the BL-4CT: After fitting this cell, run one full discharge to auto-shutoff, then charge uninterrupted to 100% before normal use. The Nokia fuel gauge IC recalibrates its coulomb counter against the new cell's discharge curve during that first cycle — skipping it causes early percentage jumps.

Why the Nokia 5310 reports wrong battery percentage after a cell swap

Nokia's fuel gauge IC stores a discharge curve from the original cell in non-volatile memory. When a new cell goes in, the stored curve no longer matches actual cell chemistry, so the reported percentage drifts — often reading 40% when the phone is close to cutoff voltage. The fix is a full recalibration cycle: discharge completely until the phone shuts itself down, then charge to 100% without interruption. After that single cycle, the coulomb counter maps against the new cell and percentage reporting stabilises.

Sudden shutdown at 20–30% on the replacement cell

This happens when the fuel gauge IC is still reading from the old cell's calibration data and the phone hits the hardware low-voltage cutoff — typically 3.2V on Nokia's BL-4CT BMS — before the OS registers a low battery warning. The cell voltage collapses faster than the uncalibrated counter expects under screen or call load. Run one complete discharge-to-shutoff cycle followed by a full uninterrupted charge. If shutdowns persist after two full cycles, measure resting voltage after shutdown — a healthy cell should read above 3.3V at the hardware cutoff point.