I've certainly been burned by crew installing batteries incorrectly, especially on BTR packs (two classics: putting one of the six batteries in backwards, or, putting one in with the pull strap between the battery and its terminal...both will make the pack run long enough to test it 
). Are you sure they were both in the right way around when you first opened the pack? Or, did they get mixed up and put one old and one new battery in (I know they both metered the same, but...). I would put this one down to crew error and keep an eye on it...as you are.
I am 99 percent sure that the Shure UHF-R packs won’t even turn on if the batteries are flipped. And I also looked when I pulled them out. They were in correctly. Our battery handling procedure is pretty tight all of the old batteries are removed after a do an individual check of each pack to make sure there is no issue with the microphone and its wire to the pack itself. Then only after all of the old batteries are removed are they given the new batteries to put in. I have thought about reversing the check to after the new batteries are put in but that means more time used up on the new batteries. Sometime hopefully soon I am planning on testing some rechargeable because of how many batteries we use per show. I know that adds a whole bunch other battery handling issues.
