Re: Why does my galaxy S3 mini say it is charging, when not attached to charger
There's an intermittent short in the charger port - usually some tiny piece of conductive dirt. Sometimes just a puff into the port will blow it out. If not, a strong light, a good magnifying glass (and good eyesight, or borrow someone who has), a pointed wooden toothpick and some rubbing alcohol. On one side of the bar running down the middle of the charging port are tiny metal contacts (the side of the port that's shorter). Dip the toothpick into the alcohol and very gently run it down between the first pair of contacts. Swish it in the alcohol and do it to the space between the second and 3rd contact. Etc. Then blow into the port a few times to dry the alcohol. Turn the phone on and it shouldn't indicate charging.
If it still does, the short could be in the port itself, and it'll have to be replaced (by a shop - please don't try doing it yourself, you'll most likely turn a cheap repair into a major disaster if you don't have experience.)