About this replacement
Asus X405 / ZenBook X405U Series — 11.52V Li-Polymer Replacement Battery (0B200-02540000)
This 11.52V 3600mAh (41.47Wh) lithium-polymer battery replaces the original cell in the Asus X405, X405UR-3B, ZenBook X405, and ZenBook X405U series notebooks. Part numbers 0B200-02540000 and B31N1632 (3ICP5/57/81) both apply to this line. It slots into the same bay as the factory unit and connects to the same BMS header.
- X405 and ZenBook X405U platform compatibility: These models share a 3-cell 11.52V architecture, the same physical connector, and an identical BMS handshake protocol — which is why one cell covers the full X405 range without hardware modification.
- Bench tested on actual hardware: We ran this cell through charge, discharge, and BMS communication checks on X405U hardware. The BMS recognised the cell, reported state-of-charge correctly, and charge termination triggered cleanly at capacity.
- Post-install calibration on the X405: After fitting this battery, run one full discharge to hibernate-cutoff, then charge uninterrupted to 100%. This resets the BIOS battery learn cycle and clears the inaccurate health warning that appears after every cell swap on this platform.
BIOS reporting poor battery health immediately after fitting a new X405 cell
The X405 BIOS reads health data from EEPROM values written by the original cell during its service life. A new cell arrives with factory EEPROM data that does not match those stored values, so the BIOS flags it as degraded before any real use occurs. This is not a fault with the replacement cell. Run one full discharge-to-hibernate and one uninterrupted charge to 100% to allow the BIOS learn cycle to rewrite its reference data. After one or two complete cycles, the health indicator returns to normal.
X405 shutting down at 20–30% charge shown on the fuel gauge
This happens when the fuel gauge IC is still calibrated against the old cell's discharge curve. Under combined CPU and display load, the new cell's actual voltage drops faster than the IC predicts, and the laptop hits the low-voltage cutoff while the gauge still reads 20–30%. The fix is not a hardware fault — the IC needs calibration cycles against the new cell's chemistry. Let the laptop discharge fully to hibernate two or three times without interruption, then charge to 100% each time. After three cycles the gauge typically tracks within 5% of actual remaining charge.