A123 batteries are round cells and I have never seen one puff or explode. They hold the charge for a very long time. I have recharged after a few months and they hardly take any further charge if stored at full capacity as recommended. I always charge mine in the model and try to make sure I use no other batteries. I use them for fuel filler, air pump etc as well as 2 cell for Rx and 3 cell for ECU. I always charge at 4 amps so charging several planes does not take very long.

John