If the cord it came with is not charging correctly, do you by any chance have a lighting cable that you can plug into the ear pods?
If they charge completely when connected to the lightning cable, then the issue could be the charging pad itself or the placement of the earpods on the pad.
When you put it on the charging pad, the display needs to be facing up and it should be in the center of the pad.
When the charging pad is plugged in correctly, it should have green light around the edge. Once the ear pods are placed on the pad, the light should then change to blue and show on the display of the ear pods.