Why does my battery percentage keep going up and then down when i am charging it

[Ilovenikkipfahler]

See when I am charging my phone on my car charger it's charging my phone but it keeps going up then down why is it doing that

 

[Kodak2]

Is the phone just charging in the car, or are you using it at the same time for navigation or music? Depending on what power is being withdrawn from the phone whilst charging will effect the charge rate.