Q:Why are they inflating? Is it water vapors (moisture) that's building inside the cell?
A:About inflating, it's not with water vapors. As for lipo batteries, the status of inside is like" solid-state". So if the lipo pack inflating/swelling, that's due to over-charging or over-discharging which damaged the inside structure of the lipo packs materials, and caused the gas, which seems will be swelled.