When my wife used her Apple i phone last week to ring me it was raining which seemed to cause a problem even thought he phone was in it's case and now the battery does not seem able to hold it's charge for long.I have checked online and batteries are available but on checking on how to change one it seems to be a tricky job and also you seem to need some special tool(s) for the job.Can anyone advise as to what I need to do.It is a Apple i phone 4s