Watch my video of me and Matt charging 9 batteries at one time. I have done the mod to slow the fans down, and in that video, you will see that the PSU's will over ride the pin and kick the fans on high if it needs to. and even pulling a constant 30 amps out of this thing, it never kicked the fans on high for more than about 30 seconds. Mostly just pulsed them. So no issue with keeping them cool on low.