Iphone Only Charges When Off

I have an iphone 6, i added a mophie case
all works well for 6 months or so, till now

now it wont charge, unless its turned off

what happened?
can I change it?

 

Does the same thing happen when you try to charge the phone itself and the mophie case separately?

 

Have you upgraded your OS? sometimes newer version create problems.

 

Thanks guys
turns out it was the cord..got a new cord and it charges fine
why it would ONLY charge when off and NOT on, is still a mystery to me
but don't print cartridges stop printing after X pages, even though they still have ink in them?

 

If the power cord is damaged it wont charge no matter whether on or off.
If you read the support guide at Mophie it tells you clearly that if the charging level of either part - phone or mophie case - has fallen below a certain minimum charge level, then you must charge them separately.