About this replacement
HP ENVY X360 13-AG0500ND — 15.4V Li-Polymer Replacement Battery (HSTNN-IB8K)
This is a 15.4V, 3400mAh (52.36Wh) Li-Polymer replacement battery for the HP ENVY X360 13-AG0500ND convertible laptop and related ENVY 13 series models. It fits the slim 5.30mm cell bay used across the AG and AH chassis lines. OEM part numbers covered include HSTNN-IB8K, KC04XL, L08496-855, L08544-1C1, TPN-W133, and TPN-W136.
- ENVY X360 AG and AH series fitment: These models share the same 15.4V four-cell Li-Polymer architecture, identical connector pinout, and BMS handshake protocol — which is why one cell pack covers the AG0500ND, AG0004NG, ag0000au, and AH0001NG variants without modification.
- Bench tested on actual hardware: We ran this pack on the AG-series chassis and confirmed the BMS completed charge negotiation correctly, the EC recognised the cell as a known unit, and full-voltage delivery held steady under combined CPU and display load without triggering a premature cutoff.
- Post-install discharge cycle on ENVY X360: After fitting, run a full discharge to the BIOS hibernate cutoff, then charge uninterrupted to 100%. This resets the BIOS battery learn cycle on the ENVY platform and clears the inaccurate health warning that appears after every cell swap on these machines.
BIOS reporting poor battery health immediately after fitting a new cell
The HP ENVY X360 EC reads EEPROM data written by the original factory cell and compares it against the new pack on first boot. Because the EEPROM cycle count and learned capacity from the old cell don't match the fresh chemistry, the BIOS flags health as degraded — even when the replacement cell is brand new. This is a firmware artefact, not a fault with the battery. Run one full discharge-to-hibernate followed by an uninterrupted charge to 100% and the learn cycle rewrites the health register correctly.
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 voltage curve. The gauge still uses the old cell's discharge profile, so it misreads remaining capacity and the system hits the low-voltage hardware cutoff before the displayed percentage reaches zero. It is not a cell defect. Run two to three full discharge-and-charge cycles — by the third cycle the fuel gauge IC recalibrates and the shutdown point aligns with the correct remaining charge, typically dropping to 5% or below before cutoff.