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:
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).
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.
Li-ion cannot absorb overcharge, and when fully charged the charge current must be cut off. A continuous trickle charge would cause plating of metallic lithium, and this could compromise safety.
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:
Once the battery is 'full' (=current cut off) the saturation is recalculated to represent the actual charge.
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