Like I said, I don't use electronics and even if I decided to get fish finder/GPS, I'd make do with lithium batteries for a little as I would use them.

Idea was just a out of the box thought, an alternative to solar.
My idea wouldn't be something you kept mounted permanently, something you would put in water if/when you need power. People paddle with outboard mounted fish finder transducers. If done right, I don't think the drag would be a big factor, especially in a tandem setting.

You could probably adapt to use with any running water source in or near camp?

I agree, solar will probably be in all the items mentioned.
I wouldn't be surprised to see some sort of lightweight/collapsible wind powered generator being developed for back country areas.

I also like the battery charging idea using the modified hand crank flashlight.
Maybe not to recharge totally dead batteries, but to keep them topped off.  Siting around campfire at night a few minutes of cranking right/left hands would keep the rod/reels muscles in fine tune ;)