RE: air bubble in etec lipo? dangerous?
The cell is bad!
I just ran into this with a Thunder Power 2100 pack.
Not recommended!!! but I had to see so I disassembled the pack.
I found that the cell was leaking past the Silver barrier and had acid damage in a corner and along the seam.
I posted a photo on R*Groups and someone told me to wrap it well and send it back as they would replace it from the photos I took.
The cell had never been dropped or in a crash, it looked like the shrink wrap had damaged the seams when it was shrunk. 1 month old.
The bad cell had 4.2 volts on it and the other good cell 4.3 volts so they were balanced.
I would not take the chance with it either dispose or send it back.
Another indicator is if you store your cells in safe metal container , a leaking cell has a sweet smell to it when you open the container.