I hear the fan every time it's charging. I was doing some things in the garage once and felt the fan was coming on pretty regularly, so I started timing and noticed it would come on about every two minutes for about 8 seconds. Sometimes it would come on for just a couple of seconds, but overall it's pretty regular. It was hot in the garage that day, but I've also noticed it when it's not really hot at all, though I haven't timed it. I imagine that if it's cold, the fan might not need to come on. That fan could be one of the reasons the efficiency for charging is not as good on Level 1 as Level 2, since it takes the car much longer to charge, and therefore the fan will come on more times. Has anyone charging on Level 2 noticed how frequently and for how long the fan comes on to cool the battery?