About this replacement
Toshiba Satellite S55t / L55t / P55 Series — 14.4V Li-ion Replacement Battery (PA5107U-1BRS)
This is a 14.4V, 2830mAh (40.75Wh) lithium-ion battery for the Toshiba Satellite S55t, L55t, and P55 series laptops. It replaces OEM part PA5107U-1BRS and fits the connector and bay geometry of all S55t, L55t, and P55 variants listed above. Install it when the original cell no longer holds charge or the laptop requires AC power to function.
- S55t, L55t, and P55 platform fit: These three series share the same 14.4V four-cell battery bay, connector pinout, and BMS communication protocol — which is why one part number covers all of them. The SMBus data lines carry fuel gauge and health data the same way across every chassis variant.
- Bench tested on actual hardware: We seated this cell in an S55t chassis and cycled it through charge and discharge under CPU and display load. The BMS handshake completed without fault codes, and the charge controller accepted the full 40.75Wh capacity without interruption.
- Post-install calibration on the S55t: After fitting this battery, run one full discharge to hibernate-cutoff, then charge uninterrupted to 100% without unplugging. This gives the Toshiba BIOS fuel gauge IC a complete voltage curve to map against the new cell and clears the inaccurate health warning that appears after every cell swap.
Why the S55t BIOS reports poor battery health immediately after a cell swap
The Toshiba BIOS reads health data stored in the battery's EEPROM, not from live cell measurements. When you fit a new cell, the EEPROM contains factory-default values that don't match the BIOS's learned cycle history for the old pack. The system flags this mismatch as degraded health. Running one full discharge-to-hibernate followed by an uninterrupted charge to 100% forces the fuel gauge IC to rewrite its internal state against the new cell's actual voltage curve. After one or two complete cycles, the health indicator normalises.
Satellite S55t shutting down at 20–30% charge shown on screen
This happens when the cell can't sustain voltage under combined CPU and display load — the real terminal voltage drops below the BMS cutoff threshold even though the OS gauge still shows charge remaining. It's a calibration gap between the fuel gauge's estimate and actual cell behaviour, common after any cell replacement. The fix is a calibration cycle: drain the laptop to automatic hibernate under normal use, leave it off for 30 minutes, then charge to 100% without interruption. After two full cycles, the fuel gauge IC recalibrates its discharge curve and the shutdowns stop occurring above 10–12V terminal voltage.