That's kind of the problem with this silly race to the thinnest notebook, batteries keep getting smaller or manufacturers switch to more frugal/weaker processors like the Core M to save on power.It's only a cross if it actually has a good performance.
Seems like a 12 incher you keep plugged in all, most of the time to me; a kind of throwback to old timey laptops.
Neither is a good compromise to me, I want a capable processor and 9-10 hours of autonomy - the thickness of the thing is secondary (within reason).