Lazi I haven't seen the charger version but I would guess it has to use the batteries for the USB charger.

Its a small solar panel and I don't think ti would ahve enough juice to power a cell phone battery in a reasonable time without using the batteries.

I have a 6 watt panel that works great and it doesn't use batteries but it has at least 6 times the surface area if not more than the Waka Waka.