Charge % less than 100% even overnight?
You should try to completely unload your iPhone. Let it go to 0 % (and shut down from itself), then plug it and let it charge completely. It should fix your problem.

See this articles from Apple for more information:


http://www.apple.com/batteries/iphone.html
http://support.apple.com/kb/ht1476


The gists you need:


  For proper maintenance of a lithium-based battery, it’s important to keep the electrons in it moving occasionally. Be sure to go through at least one charge cycle per month (charging the battery to 100% and then completely running it down).