My iPhone mini lasts about 6 hours. If I hike in the cold it lasts maybe 2.5 hours tops, and hikes are usually 4-6 hours total, so it's usually dead by the time I'm done, and so I can't tap to ride the train home unless I bring a power bank.

If I have a long train ride, like 2 hours, and I read on it, it'll usually use about 50% of the battery in that duration.

If I go somewhere new, and use google maps a lot to navigate around, it'll last about 3 hours total.

If I go somewhere with bad cellular signal, it constantly fights to connect and drains incredibly quickly, often in a matter of 2 hours.

The Air looks like it's supposed to have a battery that's about 30% larger than the mini's, and the mini is wildly insufficient for regular use.