ORIGINAL: Red Scholefield

Sorry, but a good Ni-Mh battery that is unformed can gas and vent if it is hit with an abusive charge rate of nearly 1C. Since the material has not been properly formed it cannot accept charge at these rates. The energy going into the cell then goes to heat which can cause the electrolyte to boil - which results in venting as evidenced by the "sizzling/bubbling noise" noted by the user.