The HP BF04043XL is an internal lithium-polymer battery for compatible laptops, listed as an original HP part. It is designed to fit inside a compatible notebook as a replacement battery.
Its stated capacity is 43.7 Wh (5685 mAh), with a 7.7 V output and 4 cells. These specifications identify the BF04043XL variant.
The listing names HP Spectre 13-af000 and HP Spectre 13-af100 among suitable models, so check the exact laptop model for compatibility.