W840BAT-4 Schenker S405 Laptop Replacement Battery 15.12V 2700mAh

Schenker S405 — 15.12V Li-ion Replacement Battery (W840BAT-4)

This is a 15.12V, 2700mAh (40.82Wh) Li-ion battery for the Schenker S405 notebook. It replaces OEM part numbers W840BAT-4, 6-87-W840S-4DL1, and 6-87-W840S-4DL2. Fit the battery and the S405 runs on internal power as it did from new.

• S405 platform compatibility: The S405 shares a common battery bay and connector across its variants. All three OEM part numbers reference the same 15.12V four-cell configuration, so one replacement covers the full S405 range without adapter or modification.
• Bench tested on actual hardware: We cycled this cell on the S405 platform and confirmed the BMS handshake completes correctly. The notebook exited standby without error, and charge acceptance held steady from the first cycle through full capacity.
• First-cycle calibration on the S405: After fitting, run the laptop on battery until it hibernates at the low-voltage cutoff, then charge uninterrupted to 100%. This single discharge-charge cycle resets the BIOS battery learn cycle and clears the inaccurate health warning the S405 routinely throws after any cell swap.

BIOS reporting poor battery health immediately after fitting the W840BAT-4

The S405 BIOS reads health data from EEPROM registers written by the original cell during its service life. A new cell arrives with fresh EEPROM data that does not match the history the BIOS expects, so it flags the battery as degraded before a single charge completes. This is a firmware interpretation issue, not a cell fault. One full discharge to hibernate-cutoff followed by an uninterrupted charge to 100% allows the BIOS learn cycle to overwrite the stale register values. After that cycle, the health indicator should return to normal.

S405 shutting down at 20–30% shown on the fuel gauge

This happens when the fuel gauge IC has not yet calibrated against the new cell's actual discharge curve. The gauge was mapped to the old, degraded cell and predicts a voltage floor that no longer matches reality — so the system shuts down while the gauge still shows charge remaining. Run two full discharge-to-hibernate and charge-to-100% cycles back to back. After the second cycle the fuel gauge IC re-maps its curve to the new cell and the reported percentage at shutdown should drop to below 5%.