No charging LED on Argon when charging

I have a strange one. I have a mesh consisting of an Argon and 4 Xenons. I just got some LiPo batteries for them. The Argon did not have the charging LED lit so I assumed the battery was fully charged. I left it running on the battery only and after a few minutes it died. I plugged back into USB and it appeared it was not charging at all. Long story short - after doing some troubleshooting it turns out that it is charging. It’s charging but the charging LED never comes on.

ideas or thoughts ?