Wow - almost a 40% drop in capacity over a five year period? That's kind of disquieting. I hope the Niro batteries fare better than that.
I live in Southern CA and in terms of climate considerations, I'm contemplating if I should even attempt to charge my batteries on the days when the garage is regularly over 100 F. But if I was in a more northern climate, I'd be tempted to charge during the winter months shortly after I got home and before the batteries had a chance to cool off more than a little because I've read that you can do damage to Lithium Ion batteries if you attempt to charge them below 0 C (32 F). I wonder if that general guidance applies to Niro batteries, or if the Niro engineering has found some way to prevent them from being damaged when confronted with a cold climate.
2018 Niro PHEV Gravity Blue