Thought I would come back over here for a while and see what is going on.
I have given up trying to explain that Yamaha's do not actually have an alternator as that term is generally understood by the masses. If I used the term permanent magnet generator many would not understand. Maybe your choice of words are the best. A battery charging system. I guess that is why the question is being asked.
And yes it is highly desirable for us to know the actual model of the motor. But you know as well as I that that rarely ever happens. Even if we ask for it. Now in the case of the F25, all models issued for 2013 have battery charging capability. Absolutely the US models. I am guessing that all models. Even the Enduro 25.
Check out the Enduro models. Some three cylinders with one carburetor. Look at the compression ratio of the Enduro 75. 100/1 oil on some.
http://enduro.afmotorscuracao.com/