I phone 5 battery drains while plugged in

My I Phone 5 battery drains while plugged in to a wall outlet. Wish to frame and limit this discussion to the fundamental questions (please nothing relative to applications or modes of operations) and only identical (not just similar) symptoms. The question is, is it ever normal for the I PHONE 5 to consume power at a rate faster than can be restored by charging? Looking for conclusive pro responses here...thanks for understanding. 😊