A31-U20 Asus U20 Replacement Battery 11.1V 4400mAh

Asus U20 / U50 / U80 Series — 11.1V Li-ion Replacement Battery (A31-U20)

This 11.1V, 4400mAh (48.84Wh) Li-ion battery replaces the original cell in the Asus U20, U20A, U50, U80, and related ultraportable notebook series. It covers OEM part numbers A31-U20, A32-U20, A32-U50, A33-U50, and several others listed above. Drop it in when the original cell no longer holds a charge or the system reports degraded health.

• U20 / U50 / U80 platform fit: These models share the same 11.1V three-cell architecture, connector pinout, and BMS communication protocol — which is why one cell covers the full range. Voltage rail and thermistor wiring match across all variants listed.
• Bench tested on actual hardware: We ran this cell through full charge and discharge cycles on a U20A unit. The BMS handshake completed on first connection, charge acceptance was normal from empty to full, and the protection circuit tripped correctly at the low-voltage cutoff threshold.
• Post-install calibration on the U20: After fitting, run the battery down until the laptop hibernates at near-zero, then charge uninterrupted to 100%. This forces the BIOS battery learn cycle to reset against the new cell and clears the inaccurate health warning that almost always appears after a cell swap on this platform.

Why the U20 BIOS reports poor battery health immediately after a cell swap

The U20 stores battery health data in EEPROM on the original cell. When a new cell goes in, the BIOS reads stale cycle count and capacity data left over from the old pack and flags the battery as degraded before a single charge has completed. This is not a fault with the replacement cell — it is a data mismatch. One full discharge-to-hibernate followed by an uninterrupted charge to 100% resets the learn cycle. After two to three calibration cycles, the reported health figure normalises.

U20 shutting down at 20–30% remaining shown on the gauge

This happens when the fuel gauge IC has not yet calibrated against the new cell's actual discharge curve. The gauge inherited calibration data from the old, degraded pack — so it misreads the voltage cliff on the new cell and triggers shutdown earlier than the true empty point. It is not a defective battery. Run two to three complete discharge-to-hibernate and full recharge cycles without interrupting the charge. After calibration, the cutoff point shifts back to the correct low-voltage threshold near 10.5V per cell group.