To test that I would need to acquire a stack of CR1220 batteries, a couple battery holders that I can get leads on, and a couple more of those SMT LEDs (I can imagine at least one going poof while testing this kind of stuff). I only have stacks of CR20xx here at the moment. I'll try to remember to add that to my next order so I can play around with it a bit.
I wonder what the internal resistance profile is for various discharge rates. I'll need to find some data sheets on the specific battery brand if they even have any. This is sort of getting into organic chemistry land. Lithium/manganese dioxide (Li/MnO2) electrodes with an organic electrolyte. I'm sure someone has figured it out already and wrote it down, just need to find it.
Apparently these batteries are covered under the standard ANSI C18.3M, Part 1-2008 ($85 if you want an official copy, don't waste your money it's not worth it, I have a copy). It doesn't specify any internal resistance values to be followed, only the certification values. So the battery needs to be able to drive a 62k ohm load 24 hours a day for 750 hours to qualify. Cutoff voltage is 2.0V (from starting point of 3.0V). There is an integral to figure that out and I don't want to hurt my brain right now, so that is about 36mAh at a 48μA draw.
Once I get some goodies I'll play around with it.