Whenever I charge my Niro PHEV's battery a green light appears on the dash near the windshield. That appears to be routine for charging the battery. When charging is complete, the green light turns off. But I've noticed the green light appearing a few times while not actively charging the battery. I'm wondering what else would cause the green light to appear?
Read your 2018 Niro PHEV Owner's Manual.
On page H36: "The Aux. Battery Saver+ relies on the high voltage battery to charge the 12V battery. The charging indicator lamp will blink rapidly when this is occurring."