I have a 64GB 6S. My free space had been dropping much quicker than i thought it should, even with the photos i was taking. I was down to 4GB free space. Only a week or so previous I was at 9GB and i really don't think i'd taken 5GB of photos. So last night i'm at 4GB free, right? I erase my phone, all content & settings but right before i do that i back the phone up. Today i send the phone in for a new battery as i intend on keeping it a few more years. I get the phone back and then i go to restore from backup. I now have 17GB free space and i've no idea how. I've had a look and all my photos SEEM to be on the phone. All the apps that were there appear to be there. Nothing appears to be missing (not to say that there isn't anything missing, but i have over 4000 photos so i can't really go through 1-by-1. I'm just wondering if some knowledgable soul could explain how 13GB has just appeared out of nowhere.