Hello, I have the same charger. And mine does the same but only 1 pack vents. My batteries at the most get about 3 to 5 degree's hotter than they should be but my packs are over 2 years old and I charge at 5.5amps with a cutoff of 5mv/cell. The way it charges if U compare it this charger acually puts more in the cells. I compared it to my Pulsar Comp and the Quasar Pro I have. I have 1 pack that takes over 4000mah with this charger. I am also using Pro-Match batteries right now. I really don't think it's the charger, but if U feel it is U can always goto integy web site forums and ask Arthur about it.
Bob