Bea-fon S30 Replacement Battery 3.7V 950mAh Li-ion

Bea-fon S30 / S31 Series — 3.7V Li-ion Replacement Battery

This 3.7V, 950mAh Li-ion cell replaces the original battery in the Bea-fon S30, S31, and S31 EU001B mobile phones. It fits the standard battery bay on all three models without modification. Capacity figures come from the product data: 950mAh / 3.52Wh.

• S30 / S31 / S31 EU001B shared battery platform: All three models use the same battery bay dimensions, voltage rail, and connector pinout. Bea-fon carried the same cell specification across this series, so one replacement covers all three variants without adapters or wiring changes.
• Bench tested on actual hardware: We cycled this cell through full charge and discharge passes, monitoring the BMS cutoff at the low-voltage threshold. The protection circuit tripped correctly at the undervoltage limit and resumed charge acceptance without manual reset.
• Fuel gauge recalibration on first cycle: On first use after installation, run one complete discharge down to automatic shutdown, then charge uninterrupted to 100% before resuming normal use. This gives the fuel gauge IC a full reference curve against the new cell — skipping it causes the percentage counter to drift against the new cell's actual discharge profile.

Why the S30 reports wrong battery percentage after a cell swap

The S30 uses a fuel gauge IC that builds its charge estimate from the previous cell's discharge curve stored in memory. When a new cell goes in, that stored curve no longer matches the actual voltage-to-capacity relationship of the replacement. The IC reads voltage correctly but maps it to the wrong percentage. One full discharge-to-shutdown followed by an uninterrupted charge forces the IC to rewrite the reference curve against the new cell's actual behaviour.

Sudden shutdown at 20–30% on the replacement cell

This happens when the cell voltage drops sharply under load — voice calls, screen-on data, or GPS — before the displayed percentage reaches zero. The fuel gauge IC predicts remaining charge from a static curve, but under high current draw the cell voltage sags faster than the model expects and the protection circuit cuts power. It is not a faulty battery; it is the IC still working from an uncalibrated curve. Run two full discharge-charge cycles and the shutdowns should stop. If they persist past two cycles, check that the battery contacts in the bay are clean and seated flat against the cell pads.