Hi, I got my daughter a 4th gen iPod touch for Christmas, but I'm finding the battery life quite disappointing. I've replaced the battery, but it's still bringing up the 20% warning quite soon if she's watching a film or playing games. I was looking for a case with a built in external battery, but can't seem to find any. I've seen mention of a Mophie Juice Pack air, but can't find any for sale anywhere. Can anyone give any advice on any alternatives? Thanks.