It doesn't.
Sounds like the charging light or icon has just not turned off (sometimes my old phone's charging light would stay on after I removed it from the charger, though waking the screen up would clear that). Try rebooting the phone, and that should clear it.
If not, have a look at the charging port to make sure there's nothing stuck in there. If the phone has a removable battery, pull it out and check it looks OK (if it's started to swell then you need to replace the battery). But I expect this is just a software glitch.