Why is my phone not recognising that it is charging?

Hi

Since yesterday my phone has been saying that the battery is on 74%. When I plug the charger in it says it is not charging. However, when I turn the phone off with the charger connected it says that it is charging and the correct battery level. When I turn it back on it doesn't recognise that it is charging. Why is this? I've turned to battery percentage thing on and off but this doesn't make a difference. Thanks.