On Apple’s support forums, many users are discussing various ways and sharing advice about slow charging of iPhone or iPad. Sometimes it will stop charging at all from any charging socket.
However, there are many cases when it is neither a hardware nor a software issue but rather a foreign object hindering the charging process by blocking the lightning port.
Dan Graziano from CNET offers an easy fix to this.
Most of the time the problem is caused by physical clog which might be dust, lint or debris from your purse pocket or even your own living space.
It is very easy to get rid of this clog that is present in the Lightning port. Get hold of a spear, toothpick or even an opened paperclip and VERY GENTLY use it to remove any lint that might have accumulated there inside the lightning port.
If the problem is not solved try removing any junk inside by using compressed air can to blow it away.
In other cases pay a visit to a technician who might see if it is related to a software or hardware issue.