"Adhesive on new Ifixit battery doesn’t stick. Old stock?"に関する回答Exactly same problem here. I’ve cleaned it quite well using the included adhesive remover before putting in the new battery. I think that the reason why it happens is because there is a tension created by the plastic frame of the battery, pushing against the macbook’s frame. So the battery doesn’t lay evenly and adhesive can’t do its job. I think that the adhesive layer should be much thicker to compensate it. Not sure what to do. I am afraid doing any DIY because of the high temperatures and potential expansion of the battery.