Why is my iPhone XR smart battery case having issues right out of the box?

So basically when i took the case out of the box and connected it to my phone it showed 0% on widgets so i connected it to power and suddenly it was at 78%. Then i disconnected it to power and it was again at 0%. I tried to charge the case separately over night but woke up to the same thing. If i charge the case separately it shows the orange light for a few seconds and then turns to green. Please help me to solve this problem. Thank You