Its maybe not that simple. I suggest you register on the forums (free) and post the question again in the forum for your particular device and include the following information:
Make, model and age of phone
Have you tried an different charger? Are you using the original charger - they are not all rated for the same max current.
Have you tried a different lead?
Was the phone on (maybe screen off but downloading) while charging? That would slow it down.