Bought mine Tues early evening and charged it for the first time this morning with 50% battery left. I would say it was luke warm, nothing to be concerned about. Charged using a Monoprice premium Micro USB cable connected to an Anker dual port USB charger.
That is the Way I would describe my iSticks when I charge them.
About the Same Temperature as an 18650 Battery when charged on my Nitecore Charger. Maybe a Tad Warmer because there is Less Airflow around the Battery in the istick. But Not Much more.