Apple replaced a new set of i-pod mini for me. and right now, it is happening all over again!

does anybody experience the same? i heard after the warranty is over, replacing the battery is useless and the cost is as good as getting a new set. if i send it for warranty now (2nd round of warranty), will they still fix it for me?
my friend uses Creative mp3 and her battery last for 5 days and she plays it for about 10 hours a day! is Creative or Apple a better buy in the end?
