Not sure what you mean by "external battery" - both Android and iPhone have external batteries available.
The average person has no interest any of that t
The average person has 0 interest any of that.
THIS. Core's basically a smartphone the size of a an iPod shuffle where the interface will not need a screen, and where you're expected to interact with it via voice or the 2 minimal programmable buttons (which will probably be context aware and provide even more functionality depending on what app you're using). This is why I find the whole device fascinating! The iPhone removed the keyboard, the core is removing the screen!
I also hate android for many reasons and am unlikely to move away from iPhone except to something entirely new/better than either, which doesn't particularly appear to be in the pipeline. In the next couple years I want to get rid of all uncontrolled radios on my person, though, so I'll probably be switching to a de-radioed iPhone or iPad or iPod Touch or something.