The iphone 5 has 2 replacement programs atm....for on/off button,
see here, and for battery,
see here.
We just had one replaced due to the on/off button. The replacement phones are "reconditioned" but have new front/rear glass displays and batteries.
Generally Apple have agreed that if your iphone
has a major fault in the first 2 years of it's purchase it will be replaced. Forget about the 1 year warranty they mention, it's actually recognised (by apple) as 2 years due to consumer laws.