Xiaomi MI AIR 13.3 Replacement Battery 7.7V 5200mAh R13B03W

Xiaomi Mi Air 13.3 — 7.7V Li-Polymer Replacement Battery (R13B03W)

This is a 7.7V, 5200mAh (40.04Wh) Li-Polymer battery pack for the Xiaomi Mi Air 13.3 notebook. It replaces OEM part number R13B03W directly. If your original cell has degraded or failed to hold charge, this restores cordless operation on that specific 13.3-inch ultra-thin chassis.

• Mi Air 13.3 fitment: The Mi Air 13.3 uses a narrow, slim-profile pack — 283.20 x 57.90 x 8.10mm — matched to the chassis cavity. The R13B03W connector and BMS pinout carry both charge and fuel-gauge data lines; an incorrect pack causes the EC to reject communication entirely.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the Mi Air 13.3 platform and confirmed the BMS handshake with the embedded controller. The protection circuit responded correctly to both charge termination and low-voltage cutoff events.
• Post-swap calibration on the Mi Air 13.3: After fitting, run the battery down until the laptop hibernates on cutoff, 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 appears after every cell swap on this model.

Why the Mi Air 13.3 BIOS reports poor battery health after a cell swap

The Mi Air 13.3 stores battery health data in EEPROM on the original pack. When a new cell goes in, the BIOS reads that EEPROM baseline and finds no match, so it flags the battery as unknown or degraded. This is a firmware-side artefact — not a fault with the replacement cell. Running a full discharge-to-hibernate followed by an uninterrupted charge to 100% triggers the BIOS learn cycle and rewrites the health register against the new cell's actual capacity.

Mi Air 13.3 shutting down at 20–30% charge shown on screen

This happens when the fuel gauge IC is still calibrated to the old, degraded cell. The gauge reports 20–30% remaining, but the actual cell voltage drops below the minimum sustain threshold under combined CPU and display load — the laptop shuts off to protect the hardware. The fuel gauge IC needs two to three full discharge-and-charge cycles against the new cell to recalibrate its internal model. After those cycles, the reported percentage and the actual cutoff voltage align; target a resting voltage of around 7.7V at full charge to confirm the cell is healthy.