I did some research on the etrex 30s and my conclusion was the removable AA batteries were not really going to be an advantage in a touring world where I'd be charging my mobile phone, headphones and usb lights anyway.
An inexpensive 10k mAh powerbamk is definitely the way to go. You could charge the Explore 10 times on one of these before needing to hit a wall socket.
You can also use the Explore as a normal GPS for hiking I suspect. Not sure if the maps lack specific details compared to the etrex. The default European maps seem very detailed and based onthe OpenStreetMap overlays.