I ran some tests on the capacity of old Eneloops vs new (standard) Eneloops, and I thought the findings very interesting.
The old Eneloops are from June 2006, so 12 years old. The new ones are just a few months old, fresh out of the package.
First, the new ones. I did discharge capacity tests on four AA’s and four AAA’s. (At a 250mA discharge, down to 0.9v.)
For the AA’s, the first cycle average is 1917 mAh.
The second cycle average is 1972 mAh.
So, cycling increased their capacity by 2.9%. Not much, but perhaps worth doing if you want to squeeze the most out of them.
For the AAA’s, the first cycle average is 754 mAh.
The second cycle average is 778 mAh.
A 3.2% gain in capacity by cycling. So, similar to the AA’s.
Finally, I ran capacity tests on eight AA’s that are 12 years old. Probably around 200-300 cycles on them.
The average was 1852 mAh. The lowest value was 1797 mAh.
That means that Eneloops only lost 6.1% capacity after 12 years of use! Assuming they had the same initial capacity as my new cells, after a couple of cycles.
I was expecting 20–30 loss in capacity, but they’re holding up extremely well. They can still be used for high-drain lights, though their internal resistance is noticeably higher than new cells.
With results like that after 12 years, I expect I’ll still be using them after 20 years.
I have NiMH cells that are a bit older than 2006 (which is when I switched over to Eneloops), but all of them have internal resistance ridiculously high, so are only useful for very low-drain applications. Their capacities average around 1000mAh.