Swelling is not normal at all. Swelling is a sign of the battery being over charged or over discharged. In your case based on what you wrote, likely an over discharge. During charge or discharge it is normal for the battryies to get warm but not hot as you describe. The heat is a sign of over charge or discharge and is what is causing the swelling. There is a pressure build up. Since I have no clue what the individual cell voltages are or what is going on inside your batteries what I have mentioned is as good as it gets. Also, I believe I mentioned earlier that a good LiPo system often mmonitors temperature during charge cycles. Swelling and excessive heat are not normal.
Ron
Ron