I use two 13" Macbook Airs. One is an 1.3 GHz i5 from 2013 which is admittedly slowish at times with heavy Atom and browser use. The other is an 2.2 GHz i7 from 2015 and that one is pretty awesome.

The batteries on those machines are amazing. They really last for 7-9 hours depending on use. The 2013 one is starting to show the "Service battery" warning every now and then but no performance degradation is noticeable yet. It's been through 380 cycles so far.

If you use a non-Retina Macbook like those, I suggest using a bitmap font for programming (I'm using Terminus myself). It's totally sharp and easy on the eyes. Crank up the contrast in your editor's color theme and you're all set.