How much will the lithium battery cost to replace?

You have a two-year warranty on the battery, which if it fails somehow it's free of charge. Our phase-change material ensures a battery life that is much more reliable than the alternatives, but after something like 1000 cycles (40,000 miles) the battery not hold the same amount of charge as when it was new. The replacement cost today is roughly $1000 but costs are constantly coming down, so assume in 5 years something like $500.