BL-5B Yashica Replacement Battery 3.7V 750mAh Li-ion

Yashica Nokia BL-5B — 3.7V Li-ion Replacement Battery (BL-5B)

This is a 3.7V, 750mAh Li-ion cell replacing the original Nokia BL-5B battery. It fits Nokia smartphones that shipped with the BL-5B from the factory. Physical dimensions are 46.20 × 34.14 × 5.68mm — confirm these match your current cell before ordering.

• Nokia BL-5B platform fit: Nokia built several mid-range handsets around the same BL-5B form factor and 3.7V power rail. The shared footprint, connector tab placement, and cell voltage mean one replacement cell covers the entire BL-5B device family without any modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on BL-5B compatible hardware. The BMS accepted charge current cleanly, voltage held stable across light and moderate screen loads, and the protection circuit tripped correctly at the low-voltage cutoff threshold.
• Fuel gauge recalibration on first install: On first use after fitting, run one complete discharge from 100% down to automatic power-off before recharging fully. This lets the phone's fuel gauge IC map the new cell's actual discharge curve and report accurate percentages going forward.

Why the phone reports wrong battery percentage after fitting a new BL-5B cell

Nokia's fuel gauge IC stores a learned discharge curve from the original cell in memory. When a new cell with a slightly different internal resistance and discharge profile is fitted, the stored curve no longer matches the real voltage-to-capacity relationship. The phone reads voltage and maps it against the old curve, so the percentage shown is often off by 10–20%. One full discharge-charge cycle forces the coulomb counter to re-anchor its calibration to the new cell.

Sudden shutdown at 20–30% remaining on the new cell

This happens when the fuel gauge IC is still running the old cell's curve and the phone hits a voltage cliff earlier than the percentage display suggests. Under load from the modem or display backlight, the cell voltage drops faster than a fully calibrated gauge would predict, triggering a protective shutdown before the displayed percentage reaches zero. It is not a faulty cell — it is an uncalibrated gauge. Run one complete discharge to power-off and a full charge back to 100%, then check whether the shutdowns stop. If the cell voltage at shutdown is above 3.4V, the gauge is still recalibrating.