It is probably not a good idea to put a fan on the batteries themselves. This eliminates the false temp peaking but can lead to overcharging of the cells as the voltage peak can be delayed due to active cooling. To avoid the false temp peak, set the temp peak high and put a fan or two to blow down on the the external heatsink. This reduces the charger temperature without directly cooling the battery. The tiny internal fan is about useless by itself in outdoor summer temperatures.