If changer is good, there might be two reasons:
1. When you start charge it, your phone activate services that start to sync, upload and download many files. For example, if you sync your photo and video with social networks like Google+. It takes a lot of energy. But this process is finishing and your buttery should go up.
2. Buttery level is calculating with software. Because of marketing manufacturer wants you think that battery is better that it is. They are playing with numbers and you can see it. It is not big deal, just ignore it.
