Asus SBP-08 Smartphone Compatible Battery 3.7V 1400mAh

Asus SBP-08 — 3.7V Li-ion Replacement Battery (SBP-08)

This is a 3.7V, 1400mAh Li-ion battery for Asus smartphones carrying the SBP-08 designation. It replaces the original cell when the phone no longer holds a charge or shuts down unexpectedly. Capacity matches the factory spec at 5.18Wh.

• SBP-08 platform fit: These Asus phones share the same voltage rail, connector pinout, and BMS handshake protocol. The replacement cell runs at 3.7V nominal to match what the charge IC expects — swapping in a mismatched voltage trips the protection circuit and the phone will not power on.
• Bench tested on actual hardware: We ran this cell through full charge and discharge cycles on the SBP-08 platform. The BMS accepted the new cell without fault flags, and the charge IC held the correct cutoff voltage at the top of the charge curve.
• Fuel gauge recalibration after install: On first use, disable fast charging and run one complete discharge down to automatic shutoff, then charge to 100% uninterrupted. This lets the fuel gauge IC map the new cell's discharge curve before the coulomb counter commits to percentage reporting.

Why the SBP-08 phone reports wrong battery percentage after a cell swap

The fuel gauge IC stores a learned discharge curve from the original cell. When a new cell goes in, that stored curve no longer matches the actual voltage-to-capacity relationship of the replacement. The phone reads voltage, compares it against the old curve, and outputs an inaccurate percentage. One full discharge-charge cycle forces the coulomb counter to recalibrate against the new cell, after which percentage reporting stabilises.

Sudden shutdown at 20–30% on the new cell

This is a voltage cliff issue, not a capacity problem. Under high load — modem transmission bursts or screen at full brightness — the cell voltage drops sharply even when the reported percentage looks healthy. The phone's protection circuit reads that voltage dip as critically low and cuts power. Let the fuel gauge IC complete one full calibration cycle first. If shutdowns continue after calibration, check that the cell resting voltage measures above 3.6V with a multimeter before reinstalling.