Why do you have to swap the batteries? The batteries are the same, or at least should have the same build specs(correct me if I am wrong). It is the chips that are the only variable.
What is the justification for having to swap the batteries, without having to swap out every other component too, "scientist"?
"It is the chips that are the only variable" is merely an assumption, and if one of my students came to me with data making such a claim I'd send them back to the library to read up on the principles of science.
The battery are meant to have the same spec's, but that doesn't mean the same real-world performance. One battery could have an undetected fault that affects performance, or they could actually provide identical power output. It doesn't matter. The point is that the real-world situation is unknown, and therefore the battery needs to be eliminated as a variable in the comparisons. This can only be achieved through using the same battery to perform the test in each device. Don't blame me, that's science.