that's really a very pretty airplane.

I wonder why they didn't use fixed winglets instead of the more complicated folding wing.

@Gadgeteer - vertical winglets reduce drag through limiting the vortexes but do not provide any lift, while horizontal tips offer both.

Gadgeteer, i was wondering the exact same thing until i read the first paragraph.
"The aircraft is designed with folding wing-tips that will increase wingspan and, as a result, fuel efficiency without limiting access at airports."
maybe the folding wing is to allow a large wingspan without limiting access at airports.

Folding wing allows the wider wingspan to use conventional parking spaces at airports.

Well... might have been an obvious solution, as most carrier borne aircraft have had folding wings for exactly the same reason since maybe WW2... But full credit to Boeing for actually building a plane like this...

Awful big engines there....almost looks ugly.

Boeing developed a folding wing tip for the ORIGINAL 777 back in the early 90s, because American wanted to replace their DC-10s with 777s AND fit them into the same gate space!
The wing came in THREE OPTIONS: 1) Folding, with actuator inside wing 2) Retro-fittable, but bolted down with NO actuator 3) Bolted down solid wing
When American did not place an initial order for the folding wing tip, and no-one else was interested in the weight vs gate space equation, Boeing dropped it as an option and NONE were ever made!
Deja vu all over again!

Does it still use the same type of Li-ion battery troubling 787? I assume not, then what is the main power source for on-board electronics?

@ Cliff Tsay The problem with the batteries seems to be solved. The latest problem was with a french made charger that would have had to been fixed even if the plane had lead acid batteries. every maintenance squawk on a 787 is treated like news Airbus taking years to make a permanent fix for wing cracks on the A380 gets crickets.