You didn't answer one of my original questions: are you charging from a wall outlet, or a computer USB port?
Ok, and how long is it taking to charge up to 100%, starting from around 20-30%?
Also, go to Settings>Battery while charging. Does it say "AC" or "USB" when charging from the wall? If the charging plug is faulty, it might cause the device to charge as if it were plugged into a USB port, which is much slower.
Hmm, that would have been good to know earlier. So there's a red X over the battery icon in the Notification Bar when you're charging? And it still charges up? That usually means that the charging current is insufficient, and can indicate a faulty charging cable/plug. Try a different charger.