Here is the video showing how to take out the battery from z1: https://www.youtube.com/watch?v=LAutRUkpTI4&list=PLM3XYRzu8pIHojKRWDN0JspQqgTi8cVmE&index=4
And here is the video showing how to put back the battery to z1(watch form 8:39,):https://www.youtube.com/watch?v=LAutRUkpTI4&list=PLM3XYRzu8pIHojKRWDN0JspQqgTi8cVmE&index=4
( to reassemble the phone, you need the back cover sticker in the end: http://www.witrigs.com/oem-back-cover-sticker-for-sony-xperia-z1-compact)