Originally posted by Ishpuini FWIW, I do not observe any difference in performance between them yet.
It hard to tell any difference without measuring the capacity. I switch off the auto-power-off on my camera fully charge a battery and insert it, let the battery discharge. My new batteries give 6 hours from full charge to full discharge. My 2015 battery give ~ 4h50 discharge time. Hardly noticeable on mixed mode casual shooting ("I do not observe a difference"). But the 6 years old battery has about 20~25% less capacity than the new ones. The question is, even if a 2012 battery works fine now, how much capacity will remain 5 years from now. IMO, they should sell 8 years old Li-Ion batteries as new, that's just wrong, knowing that Li-Ion battery wear out with time even if unused.