Once again, searchin the Tube, and i found this really cool homemade battery charger.
No electricity required
Well, i reckon you could do the same thing with a generator, but this is more compact.
I suggest yall check these channels out, 5tractorguy, who made this video, and Junkologists junk heap, who had the aircompressor video, along with a bunch of other really cool and odd ball tractors, engines, and miscellaneous motor stuff.
Roll the clip!