Since i hardly ever use a Thinkpad off from the electric grid, being rarely on the road or similar circumstances, there is nothing to contribute about this from my side.

But judging by the general hearsay in this matter, nothing beats those ARM Macs in regard to performance per Watt and battery live. If this angle is considered the most important view point, than there probably is no suitable Thinkpad replacement for such a Mac.

But if anything else is more important than this particular perspective, than Thinkpads are the better option regarding Linux & Windows support, upgradability & repairability, keyboard (Trackpoint!) and I/O options. And they are way cheaper, too.

Try one and compare yourself.