My launch Space Grey did this. It would never charge to 100% always between 99%-96% if I restarted the phone just by turning it off normally it would show 100%.
Decided to sell it and get a Sliver 5s it charged normally, always to 100%.
Unfortunately I had a problem with the screen clicking.
The replacement one is exhibiting the same tendency as the Space Grey I had.
All phones were restored in the same way. From an iCloud backup.
Can't say it bothers me too much, since I'm not seeing any repercussions to battery life.