would a battery replacement be possible?

@matfrags …i believe what you are looking for does not exist. there are comparisons all over the web i.e:

https://socialcompare.com/en/comparison/...

but this is not what youre looking for by my reading. best course of action is to google a replacement battery for each of the devices and hopefully one of the vendors you find list the dimensions of the actual battery. other than that, measure your battery and when you go to buy one, ask the vendor to measure theirs and compare. good luck

I think they are the same size (physically) so it should be possible. I am looking for an answer on this question as well. Both batteries run on same voltage and both have the same shape size and same connector. If you succeeded in installing 11pro max battery in an XS max please let us all know! That would be an awesome upgrade for every XS max user, including me !