How do I know battery replaced in my iPhone se original

If your battery was replaced by an Apple store or Apple authorized service center, then it is an original battery. If it was not replaced by them, then it may not be an original battery.

iPhone uses built-in, high-quality lithium-ion batteries. ... They're rigorously designed, tested, and manufactured to meet Apple quality and performance standards. These genuine Apple batteries have also been certified for safety.10-Feb-2021

About genuine iPhone batteries - Apple Support