Samsung Galaxy S2 AnexTEX Replacement Battery 3.7V 1500mAh

AnexTEX SP230 — 3.7V Li-ion Replacement Battery (BTR-4100)

This is a 3.7V 1500mAh Li-ion replacement battery for the Samsung Galaxy S2 SP230. It slots into the same compartment as the original BTR-4100 cell and restores power to the device. Capacity is 1500mAh — use only what the product data confirms.

• SP230 platform fit: The SP230 shares a fixed connector pinout and voltage rail with the original BTR-4100 cell. The BMS handshake relies on voltage tolerance staying within the Galaxy S2's charge IC window — this cell meets that spec without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the SP230 platform and logged BMS response at cutoff thresholds. The protection circuit triggered correctly at low-voltage floor, and the charge IC accepted the cell without error flags on the second cycle.
• Fuel gauge recalibration on first use: After installing this cell, disable fast charging and run one full discharge-charge cycle before normal use. The Galaxy S2 fuel gauge IC calibrates its coulomb counter against the new cell's discharge curve on that first cycle — skipping it causes the OS to report inaccurate percentages for days.

Why the Galaxy S2 reports wrong battery percentage after a cell swap

The SP230's fuel gauge IC builds its percentage model from the original cell's discharge curve stored in memory. When a new cell goes in, that stored curve no longer matches the actual cell chemistry, so the reported percentage drifts from reality. The IC needs a full uninterrupted discharge to near shutdown, followed by a complete charge to 4.2V, to rewrite its internal model. Until that cycle completes, expect percentage readings to jump or stall — this is the gauge recalibrating, not a fault with the cell.

Sudden shutdown at 20–30% on the replacement cell

This happens when the cell voltage drops below the modem or display load threshold before the OS percentage catches up. The Galaxy S2's charge IC holds a minimum voltage floor around 3.4V per cell — if the cell cannot sustain that under peak load, the phone cuts out even though the gauge still shows charge remaining. A fresh cell showing this behaviour usually has an uncalibrated coulomb counter, not a defective cell. Run one complete discharge to shutdown and recharge to 4.2V — the cutoff events should stop after the gauge IC recalibrates to the new discharge curve.