When I charge my iPhone 4s it reaches 100%. But often, in the morning, it is as low as 95% and most of the time it shows less than 100%. If I unplug it and then plug it in again it quickly reaches 100% again. How to fix? Not a problem?
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:
The gists you need:
I noticed this on my 4s too. Try this: keep the phone plugged into its charger, wake it up and let it sit for a bit awake. It should pop up to 100% pretty quickly.
I'm guessing, but I don't know for sure, that this is yet another bug in the battery/charging routines in iOS 5.0.1 and will get fixed at some point.
The iPhone 4s has a Li-ion battery.
It's important to know that once the charging process is completed, the battery is never actually full. There's always a bit of 'space' left. If you keep reconnecting your phone and charging it again for several times, you can increase the charge. This is called bump charging.
I would assume that Apple engineers changed the calcuation for the saturation of charge. The way the iPhone 4s behaves now is what the Nexus S has had already:
I'm sure Apple wanted to show the 100% in the past in order to mute customer worries. However, this 'new' behavior is totally normal and more realistic.
For more infos about Li-ion battery, and measuring charge saturation see this link. http://batteryuniversity.com/learn/article/charging_lithium_ion_batteries