About this replacement
Toshiba Tecra M7 / Portégé M700 Series — 10.8V Li-ion Replacement Battery (PA3128U-1BRS)
This 10.8V, 4400mAh (47.52Wh) Li-ion battery replaces the original cell in the Toshiba Tecra M7-ST4013, Portégé M700-S7004X Tablet PC, Portégé M405, Portégé M205-S809, and over 125 additional Toshiba Tecra and Portégé models. It cross-references OEM part numbers PA3128U-1BRS, PA3191U-1BRS, PA3191U-2BRS, PA3191U-3BRS, PA3191U-4BRS, PA3191U-5BRS, and the BAS suffix variants. Voltage, pin layout, and BMS handshake match the original spec.
- Tecra M7 and Portégé M700 platform fit: These models share the same 10.8V three-cell-series architecture, a common 9-pin SMBus connector, and the same BMS communication protocol. One cell part number covers the full group without any hardware modification.
- Bench tested on actual hardware: We ran this cell through charge and discharge cycles on a Tecra M7 unit. The BMS reported state-of-charge correctly, charge termination triggered at the expected voltage ceiling, and no fault codes appeared in the SMBus log.
- First-cycle calibration on the Tecra M7: After installing, run the laptop on battery alone until it hibernates from low charge, then charge uninterrupted to 100% without waking the system. 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 cell
The Tecra M7 BIOS reads health data from the battery's EEPROM, not from a live capacity measurement. When a new cell arrives, that EEPROM contains factory default values that don't match the BIOS's learned data from the old cell. The system flags this mismatch as degraded health before the new cell has run a single cycle. One full discharge-to-hibernate followed by an uninterrupted charge to 100% forces the BIOS to rewrite its learned values against the new cell's actual EEPROM data and clears the warning.
Laptop shuts down abruptly at 20–30% charge shown on screen
This is a voltage cliff symptom, not a firmware bug. Under full CPU and display load, the cell voltage drops faster than the fuel gauge IC can update its state-of-charge estimate, so the BIOS sees a critical undervoltage condition before the percentage readout reaches zero. It triggers an immediate shutdown to protect the cell. Run two complete calibration cycles — full discharge to hibernate cutoff, then full charge to 100% — to synchronise the fuel gauge IC with the new cell's actual discharge curve. After calibration, the shutdown threshold should move to below 5% at the same load.