About this replacement
Toshiba Tecra A3X-165 / M9 Series — 10.8V Li-ion Replacement Battery (PA3356U-1BRS)
This is a 10.8V, 4400mAh (47.52Wh) Li-ion replacement battery for the Toshiba Tecra A3X-165 and Tecra M9 series business notebooks. It also fits the Dynabook Qosmio F20 and over 170 additional Toshiba models sharing the same connector and voltage rail. OEM cross-references include PA3356U-1BRS, PABAS071, PABAS048, and PA3588U-1BRS among others.
- Tecra A3X and M9 platform compatibility: These models share a common 10.8V three-cell Li-ion architecture, identical connector pinout, and the same BMS handshake protocol — which is why a single cell works across the full Tecra A3 and M9 range without firmware modification.
- Bench tested on actual hardware: We ran this cell on a Tecra M9 chassis and confirmed the BMS negotiated charge cycles correctly, accepted a full charge to 47.52Wh, and passed voltage-under-load checks at both idle and peak CPU draw without triggering a cutoff.
- First-cycle calibration on Tecra models: After installing, run one full discharge until the laptop hibernates at cutoff, then charge uninterrupted to 100%. This resets the BIOS battery learn cycle and clears the inaccurate health or "unknown battery" warning that commonly appears after every cell swap on this platform.
BIOS reporting poor battery health immediately after fitting a new cell
The Tecra BIOS reads health data stored in the battery's EEPROM and compares it against its internal baseline from the previous cell. A brand-new cell carries factory EEPROM values that don't match the BIOS's learned profile, triggering a false "degraded" or "poor health" flag. This is not a fault with the replacement cell. Run a single full discharge-to-hibernate followed by an uninterrupted charge to 100% — the BIOS resets its learn cycle and the warning clears.
Tecra A3X shutting down at 20–30% charge shown on screen
This happens when the fuel gauge IC has not yet calibrated against the new cell's actual discharge curve. The OS reads a percentage based on the old cell's profile, but the new cell hits its lower voltage cliff at a different point — the laptop cuts power before the gauge reaches zero. It looks like a faulty battery but is a calibration mismatch. Complete two full discharge-to-hibernate and full-charge cycles; the fuel gauge IC recalibrates and shutdowns stop occurring above approximately 10.8V cutoff.