About this replacement
HP EliteBook 850 G5 / ZBook 15u — 11.55V Li-Polymer Replacement Battery (TT03XL)
This is an 11.55V, 4700mAh (54.29Wh) Li-Polymer replacement battery for the HP EliteBook 850 G5 and ZBook 15u series. It replaces OEM part numbers TT03XL, HSTNN-DB8K, HSTNN-LB8H, and 933322-855, among others. The connector, BMS handshake profile, and cell count match the original HP configuration for these platforms.
- EliteBook 850 G5 and ZBook 15u platform fit: Both machines share the same battery bay dimensions, 3-cell 11.55V rail, and HSN-I13C / HSN-I17C controller pairing. One battery covers both platforms without any hardware modification.
- Bench tested on actual hardware: We ran this cell through full charge-discharge cycles on an EliteBook 850 G5. The BMS communicated correctly with the HP EC firmware, and the fuel gauge IC registered capacity without throwing a hardware warning on POST.
- First-cycle calibration on the 850 G5: After installing, run one full discharge down 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 this platform.
BIOS reporting battery health as poor immediately after replacement
The HP EC firmware reads EEPROM data stored on the old cell during every boot. When a new cell goes in, the EEPROM signature does not match accumulated charge history, so BIOS flags the battery as degraded. This is a firmware-side artefact, not a fault with the replacement cell. Running a full discharge-to-hibernate followed by an uninterrupted charge to 100% rewrites the learn cycle data. After two to three full cycles, the health indicator normalises in both BIOS and HP Support Assistant.
Laptop shutting 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 voltage curve. The percentage reading is based on the old cell's discharge profile, so the gauge loses accuracy near the bottom of the curve. Under full CPU plus display load, the real cell voltage drops below the EC's cutoff threshold before the displayed percentage reaches zero. Run two complete discharge-to-hibernate cycles without interrupting the charge, and the gauge IC recalibrates — shutdown will align with the displayed percentage within 1–2% of actual cutoff voltage at approximately 10.8V.