I've had the mini for more than a year now... but i have the old version which has around 8 hours of battery life or less... Could I possible change the battery to the upgraded version that has 18 hours i believe? or around 16? How much would that cost me to upgrade if possible? BTW, i didn't buy the ipod at an Apple store,I got it at Marshall fields and lost my receipt. Do i send it to Apple? Thank you all for any help!