Yeah, what I've heard is that water cooling the batteries (like almost every EV does now) massively extends the life. Early Prius batteries had no cooling and the heat degraded them faster. 15 years is a pretty good life still.

On the subject of battery warranty:

The federal government requires manufacturers to offer an eight-year/100,000-mile warranty on all EV batteries. California does one better, mandating a warranty of 10 years or 150,000 miles. Some companies will cover a battery only if it completely stops working, while others will replace the battery if it falls below a certain capacity, usually 70% of the original, while still under warranty.

It's important to note, a degraded battery, even with 50% of its original capacity is still useful. Someone who doesn't need the range could drive it, or the battery could be taken apart, and have the cells repurposed or recycled. Lithium and some of the other rare metals used in batteries are quite valuable for recycling, and our abilities to do so are getting better every year.