Wow, guys you are really careful.
I cycle my batteries through all cameras they fit in. Which means coming home from a shooting any battery I had with with me, goes into the “maybe empty jar” and I grab a few to replace them in the kit from the “freshly loaded jar”. I usually take on LPE6 in the camera and 2 in reserve with me. In total I own 8 of them which means 3 get loaded over the next days and 2 are in reserve for a fast grab if two shootings are close to each other. I load them with the Hähnel Procube II which according to what I learned here in the forum is the dumbest way to do, as the Hähnel does not have much in regards careful maintenance loading. I take loving care in regards to my camery but that love does not extend to the batteries. The Hähnel can load 2 batteries at the same time and I sometimes forget the batteries for a few days in the powered up loader. However after years of that unkind loading practice I do not have any dropouts in regards to the LPE6 batteries
As I currently made space in the shelves for the upcoming R7 Mark II I only hold a R7, 1DX2 which accept the "classical Canon form factor"
However that means Canon batteries from my EOS 30D, 60D, 80D 5d Mark 1 and 5d Mark3 happily power my R7 and do not show any weakness (besides the fact that the latest version LPE6nH seems to allow maybe 50-100 shots more than the LPE6n) The LPE6 batteries I use are almost 20 years old and still do their job.
My only backup battery for the 1DX2 is the one which came with my 1D Mark4 again almost 2 decades old and still doing the job.