What kind of wall charger are you using? If it's a cheap after-market one, it could be really weak and not have the full capacity to charge an iPhone at a normal rate. This is like charging an iPad with an iPhone charger, it takes a really long time because the iPhone charger isn't designed to give the higher charge rate that an iPad requires. Just an idea, but if you have an apple charger, than maybe the charger is going like ''iphonefixer'' says. Otherwise, I'm not sure what the problem could be.
Hope this helps,
David