HP EliteBook 820 G4 Compatible Battery 11.55V 3800mAh

HP EliteBook 820 G4 — 11.55V Li-Polymer Replacement Battery (ST03XL / 821691-001)

This is an 11.55V, 3800mAh (43.89Wh) Li-Polymer battery for the HP EliteBook 820 G4 notebook. It replaces OEM part numbers 821691-001, 854050-421, 854050-541, 854109-850, HSTNN-LB7K, HSTNN-UB7D, and ST03XL. If your original cell no longer holds charge through a normal workday, this is the direct cell swap.

• EliteBook 820 G4 platform fit: All EliteBook 820 G4 variants share the same three-cell Li-Polymer pack, 11.55V nominal rail, and ST03XL connector pinout. The BMS handshake uses the same EEPROM authentication protocol across Z2V74EA, Z2V91ET, Z2V75EA, and the wider G4 lineup, so one cell revision covers the entire model range.
• Bench tested on actual hardware: We ran this cell through charge-discharge cycles on an 820 G4 unit. The BMS negotiated correctly, the BIOS accepted the cell without a hardware fault flag, and charge termination landed at the correct cutoff voltage with no thermal events.
• Post-install calibration on EliteBook 820 G4: After fitting, run one full discharge to hibernate-cutoff, then charge uninterrupted to 100%. This resets the BIOS battery learn cycle. Without it, the firmware carries over fuel gauge data from the old cell and reports inaccurate state-of-charge for the first several uses.

BIOS reporting poor battery health immediately after fitting a new cell

The EliteBook 820 G4 stores cycle count, charge history, and health metrics in the old cell's EEPROM. When you swap cells, the BIOS reads stale data and flags poor health even though the new cell is at full capacity. This is a firmware state issue, not a cell fault. Run the battery learn cycle — discharge fully to hibernate cutoff, then charge to 100% uninterrupted — and the BIOS recalibrates against the new cell's actual parameters.

EliteBook 820 G4 shutting down at 20–30% charge shown on screen

This happens when the cell voltage drops below the BIOS cutoff threshold under peak load — simultaneous CPU burst and full display brightness — before the fuel gauge reaches zero. The voltage sag is steeper than the fuel gauge IC expects because the IC is still calibrated to the degraded discharge curve of the old cell. After the post-install learn cycle, the fuel gauge maps the new cell's voltage-to-capacity curve correctly. If shutdowns persist past three full cycles, check that charge is reaching 12.6V at termination before disconnecting AC.