The battery pack would actually work well, if they weren't so hefty. The ones I've seen were around 400g, and even then you only get a few phone charges.
This weekend, I actually got to try a Garmin Edge 530. It was steeply discounted at my LBS, and the guy suggested I take it home to play with it and return it if not happy. I was very unimpressed. The poor map made me feel like I was going back to playing Space Invaders after having known Skyrim. I tried every way I could to import my routes from RWGPS, which has fantastic maps, but wasn't able to.
I need this primarily for multiday bikepacking and cross-country ski trips. There's no way I'd want to be stuck in a blizzard trying to find the trail on this unit.
I don't need this for a couple more months, so will keep an eye out for the Explore 2