Toshiba PA5157U-1BRS Satellite U40T-A Replacement Battery 11.4V

Toshiba Satellite U40T-A / M40-A / M50-A — 11.4V Li-ion Replacement Battery (PA5157U-1BRS)

This is an 11.4V Li-ion replacement battery rated at 4150mAh (47.31Wh) for the Toshiba Satellite U40T-A, M40-A, M50-A, and M50D-A ultrabook series. It replaces OEM part number PA5157U-1BRS and P31PE6-06-N01. It fits the slim three-cell battery bay used across this Satellite lineup.

• Satellite U40T-A / M-series compatibility: These models share an identical 11.4V three-cell Li-ion architecture, the same physical connector, and the same BMS communication protocol over the SMBus rail. One replacement cell serves the entire group without modification.
• Bench tested on actual hardware: We ran this cell on a Satellite M50-A and monitored the BMS handshake through full charge and discharge cycles. The BMS accepted the cell without fault codes, charge regulation kicked in at the correct 12.6V ceiling, and protection cutoff triggered at the expected low-voltage threshold.
• Post-install discharge cycle on Toshiba Satellite: After fitting this battery, let the laptop discharge completely until it hibernates on its own — do not interrupt it. Then charge uninterrupted to 100%. This resets the BIOS battery learn cycle and clears the false "poor health" or "unknown battery" warning that appears after every cell swap on this platform.

Why the Satellite U40T-A shows incorrect Wh in system information after a cell swap

The BIOS reads Wh rating from the battery's EEPROM, which stores the value written at the factory. Replacement cells may carry a slightly different EEPROM-rated Wh figure than the original, even when actual chemistry and capacity are equivalent. This is a data mismatch between the new cell's firmware and what Windows or Toshiba Power Saver expects to see. It does not affect charge behaviour or usable capacity — the displayed Wh figure updates or stabilises after one to two full calibration cycles.

Satellite M50-A shutting down at 20–30% charge shown on screen

This is a fuel gauge IC calibration problem, not a faulty cell. The gauge IC in the battery is still mapping voltage curves from the old, degraded cell, so it miscalculates the remaining charge on a fresh replacement. Under full CPU and display load, voltage drops faster than the uncalibrated gauge predicts, and the laptop hits the emergency cutoff before the displayed percentage reaches zero. Run two full discharge-to-hibernate then uninterrupted charge-to-100% cycles. After those cycles the gauge re-maps the voltage curve to the new cell and the cutoff point drops back to the correct 2–5% range.