About this replacement
Dell Latitude E5400 / E5500 Series — 11.1V Li-ion Replacement Battery (KM668)
This is an 11.1V, 6600mAh (73.26Wh) lithium-ion battery for the Dell Latitude E5400, E5500, E5410, and E5510 series laptops. It cross-references a long list of Dell OEM part numbers including KM742, MT186, RM649, PW640, WU841, and 312-0762, among others. If your original battery has degraded or failed completely, this cell matches the voltage rail, connector, and BMS handshake requirements for these platforms.
- E5400 / E5500 / E5410 / E5510 platform fit: These four Latitude models share the same battery bay geometry, 11.1V three-cell rail, and SMBus BMS communication protocol — which is why a single part number family spans all of them. The connector pinout and latch clip are identical across the group.
- Bench tested on actual hardware: We ran this cell on an E5400 and E5510 unit. The BMS handshook correctly on first insertion, BIOS recognised the battery without prompts, and charge current ramped through the expected CC/CV stages without interruption at either end.
- First-cycle calibration after install: After fitting this battery, run one full discharge to hibernate-cutoff, then charge uninterrupted to 100%. This resets the BIOS battery learn cycle and clears the inaccurate health warning that appears after every cell swap on Latitude hardware.
BIOS reporting battery health as poor immediately after replacement
Dell's BIOS stores charge-cycle count and health data in the old cell's EEPROM. When a new cell is installed, the BIOS reads no matching history and flags the battery as degraded or unknown — even though the cell is new. This is a firmware interpretation issue, not a battery fault. Run the full discharge-to-hibernate then uninterrupted charge cycle described above. After one or two complete cycles, the BIOS recalibrates and the health warning clears.
Laptop shuts 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 gauge reports 25% remaining, but the cell voltage under combined CPU and display load has already dropped below the BMS cutoff threshold — the laptop interprets this as a hard shutdown event. It is not a defective battery. Complete two full discharge-to-hibernate and full-recharge cycles, and the fuel gauge IC will map the new cell's voltage curve accurately. After calibration, the reported percentage at shutdown should align with the actual cell voltage of approximately 10.5V.