Is the (rear seat vent) Battery Fan multispeed?

You know the battery cooling fan that brings in air from the rear seat vent, I was just wondering if it is variable speed or multi-speed? What I mean is does it speed up when the batteries are hotter and slow down when they're cooler, or is it just a simple on/off type of thing.

The reason I'm wondering is because previously I'd only ever noticed it running once on a particularly hot day when it seemed to make a fairly obvious noise that was easy to notice. Recently however I've found that it seems to be running most days after driving (it's just spring here, but still summer weather for now). It does seem very quite though, so I'm thinking it might have been operating more often than I'd previously thought but I just didn't notice it before. I only noticed this a few days ago when I had to check something in the back seat and I left the car in ready mode while I did it. When my ear was close to the vent I could hear the fan was running quietly, but I wouldn't have noticed it from the drivers seat.

So would it be normal for the vent fan to run slowly and quietly a lot of the time in warm weather and only run fast and loud under more extreme conditions when the battery is really heating up?

 

Thanks Patrick.