ken white wrote:
It looks like it needs about 2-3 volts of headroom so it is probably a series regulator.
You may be better off with an old school shunt regulator and only use it when equalizing the batteries.
It's not - it's a dc-dc buck converter - even says it in the title. You can see the inductor on the board.
http://www.ti.com/product/lm2596
LandYacht - give it a try. Cheap enough and probably doesn't require that much headroom above the target voltage. Besides you could just run your fan at a slightly lower voltage if needed.