Hyundai guarantee them for 10 years and 100k in the states (8 years in europe). A quick trawl of the internet suggests that 150,000 miles is a low life expectation. Newer batteries are expected to last the life of the car >200,000 miles. Tesla batteries appear to be especially good at keeping capacity. I'll leave it to you to do your own searching if you want, but the evidence to back these figures up is out there!
I'm starting to think battery life and replacement costs should not be a major worry.