Compaq Business Notebook TC4400 Replacement Battery 10.8V 4400mAh

Compaq Business Notebook TC4400 Series — 10.8V Li-ion Replacement Battery (381373-001)

This 10.8V 4400mAh Li-ion battery replaces part numbers 381373-001, 383510-001, HSTNN-IB12, PB991A, HSTNN-C02C, and HSTNN-UB12. It fits the Compaq Business Notebook TC4400, NC4200, TC4200, and 4200 series laptops. Capacity is 47.52Wh — matched to the OEM specification for these machines.

• TC4400 and NC4200 shared platform: These models run on the same HP/Compaq mobile platform, sharing identical connector pinouts, BMS handshake protocol, and the same 10.8V three-cell-series configuration — which is why one cell fits the whole family.
• Bench tested on actual hardware: We ran this cell on a TC4400 unit and monitored BMS communication through the SMBus lines. The pack negotiated correctly with the EC, reported accurate voltage at each charge stage, and the protection circuit triggered cleanly at low-voltage cutoff.
• Post-install calibration on the TC4400: After fitting this cell, run one full discharge to hibernate cutoff, then charge uninterrupted to 100% before unplugging. This resets the BIOS battery learn cycle and clears the inaccurate health warning that appears after every cell swap on this platform.

TC4400 shutting down at 20–30% charge shown on screen

When an aged cell cannot sustain voltage under combined CPU and display load, it hits a voltage cliff well before the fuel gauge reaches zero. The BIOS interprets this sudden drop as a critical low-voltage event and forces an immediate shutdown — even though the OS still shows 20–30% remaining. A new cell with healthy internal resistance holds voltage flat under load, which eliminates this cliff. After swapping the battery, run the full discharge-to-hibernate calibration cycle so the fuel gauge IC re-maps the new cell's actual discharge curve.

BIOS reporting wrong Wh rating after fitting a replacement cell

The Wh value shown in BIOS comes from EEPROM data written to the battery pack's gas gauge IC — not from a live measurement. If the replacement cell's EEPROM was programmed with a slightly different rated figure, the BIOS will display that value rather than the actual 47.52Wh chemistry spec. This is a data mismatch, not a fault in the cell itself. To verify actual capacity, let the pack complete two full charge-discharge cycles and check the reported full-charge capacity in a tool like HWMonitor — it will converge toward the true figure at 10.8V.