Battery fan and lack of performance

I have owned a 2013 Persona for 6 years and only have 32,000 miles on it. Generally performs well. However on three occasions at least, including yesterday, it was losing performance while normal driving and trying to accelerate. Would barely move when I hit the accelerator and the fan for the battery in the back seat was roaring. After several red light stops this continued and I decided to get off the road. The car had been started from cold and sitting for hours. I pulled over and stopped, and turned off the engine. Within seconds, I turned it back on and resumed driving without the fan or any performance issues at all. This is what it did in the previous two times this happened. Plus no warning lights on on the dash. I was driving past a Toyota dealer so stopped and talked to a service manager. He had no idea...this was the same response I received in a prior inquiry more than a year ago. I don't believe the fan ducting is dirty. I never hear this fan running in normal circumstances.
Frustrating...I had even talked to a non dealer Toyota "expert"...no one has a clue.