My oldest Eneloops are from 2006, so about 13.5 years old. I have 8 of them. I ran a capacity test on all of them just last week. They average just under 1800 mAh. New Eneloops I tested are around 1950 mAh. So, about 8% capacity loss after 13.5 years. Not bad!
The lowest one tested at 1450mAh. It was much less than all the others. So, it appears to be dying, at least for higher drain stuff. But it still works fine for lower drain.
I can't accurately measure internal resistance, but the charger does show the old Eneloops do have significantly higher IR than new Eneloops. That appears to be the biggest issue with aging.
All 8 of those old Eneloops still appear to hold their charge fine, so low-self-discharge doesn't seem to be affected much.
Those Eneloops have probably been cycled 200-300 times, mostly partial discharges. So, not really heavy use, but not light either.
