@richpips – it’s certainly possible. One of the issues is charging a Li-Ion or LiPo battery from the dynamo. The output from the dynamo can vary widely in voltage and frequency, so there’s some power management to be sorted out there.
One of the things a dynamo can’t do is power a helmet light directly, but charging a battery pack during the day could be one way around that. However, you might lose gadget charging, and unless the battery is pretty large or the days are a lot longer than the nights, you’d be unlikely to get ‘all night’ burn time from the helmet light. But then, you gotta sleep sometime…
It’s also possible to run multiple dynamos by using a bottle dynamo in conjunction with a hub dynamo. You could also use solar charging during the day if the climate is suitable. Modern bottle dynamos are streets ahead of the kind of thing that was around when I was a kid, and are possibly the only way to get a dynamo onto a Jones or fatbike, e.g.
http://www.dutchbikebits.com/index.php?route=product/product&product_id=65