I don't think the iPhone Air will actually be smaller in the dimensions I care about, just thinner which I assume will compromise battery life.

My mini is holding up ok. Battery needs replacing but I haven't done it. Like mikepurvis, I carry power banks around if I'm doing anything where I'm not going to be able to recharge easily. I use one like this https://www.amazon.com/Anker-PowerCore-Magnetic-Slim-B2C/dp/...