Dell Latitude E6400 Replacement Battery 11.1V 4400mAh PT434

Dell Latitude E6400 / Precision M2400 — 11.1V Li-ion Replacement Battery (PT434)

This is an 11.1V, 4400mAh (48.84Wh) Li-ion battery for the Dell Latitude E6400, E6500, Precision M2400, and Precision M4400. It replaces a wide range of Dell OEM part numbers including PT434, KY477, C719R, and 312-0748. It fits the standard 9-cell bay on these chassis without modification.

• E6400 / E6500 / M2400 / M4400 platform compatibility: These four models share the same battery bay dimensions, connector pinout, and SMBus BMS handshake protocol — one cell works across the entire group. Dell used the same power rail design and communication stack for this generation of Latitude and Precision hardware.
• Bench tested on actual hardware: We ran this cell on an E6400 and monitored the SMBus communication during charge and discharge. The BMS reported correct voltage at each charge stage, and the protection circuit tripped at the expected low-voltage cutoff without requiring a manual reset.
• Post-install calibration on Dell BIOS: After fitting this cell, run one full discharge to hibernate-level cutoff, then charge uninterrupted to 100%. This forces the BIOS battery learn cycle to reset against the new cell's actual capacity and clears the inaccurate health warning that appears after every cell swap on this platform.

Laptop shutting down at 20–30% shown on the E6400

This is a voltage cliff issue, not a capacity error. Under full CPU and display load, an aged or uncalibrated cell cannot sustain the voltage the BIOS expects at that state of charge — so the system cuts power before the gauge reaches zero. The fuel gauge IC is still reading the old cell's discharge curve, which no longer maps to the new cell's chemistry. Run the calibration cycle described above and the BIOS will remap the curve to the new cell, pushing the shutdown point back to the correct low-voltage threshold.

BIOS reporting "battery unknown" or 0% immediately after fitting

The EEPROM data embedded in the original battery carries cycle count, health flags, and rated Wh — the new cell writes different values to those registers on first contact. Dell's BIOS reads this as an unrecognised or faulty battery and may display 0%, "unknown," or a red X on the battery icon. This is not a fault with the replacement cell. Power off completely, remove the AC adapter, reseat the battery, then boot to Windows and allow one full charge cycle to complete — the SMBus will re-initialise communication and the BIOS will accept the new EEPROM data at 11.1V nominal.