Quick look at how much have NCR18650B degraded after two years of rather light use and improper long term storage.

So, as most/some of you know according to Battery University article lithium ion batteries should be kept at ~40% of their capacity for long term storage which is around 3.82V. I have owned for about two years(ordered brand new) 8 pieces of protected Panasonic's NCR18650B batteries with claimed capacity of 3400mAh.

Upon receiving them I never tested their capacity due to lack of charger with test function for lithium batteries.

Somehow I had an impression that lithium batteries dont have considerable self discharge during storage so took it for granted that they too, just like Ni-Mh Eneloops for example, can be kept at which ever voltage I desire, thus some of them, that werent used(6 out of 8 to be exact) for about a year were kept I believe at around 80-100% of their charge, its not like they had no cycles on them, they had, but nothing that could be considered as frequent use where storing them at 100% would have negligible effect on their self-degradation.

Later on I got some more 18650 lights so some of those 6 were taken out of storage and put into use in rotation with first two.

Last november I ordered Lii-500 and decided to check out how much have these batteries lost in their overall capacity due to improper storage voltage.

Out of all 8 batteries I tested 4 that have seen, I believe, the least use, they were not marked-numbered so take these numbers with grain of salt, as I said, proper storage voltage was discovered(for me that is) last summer, so only then some of them got the proper 40% 3.82V storage numbers applied to them.

So, basically my Lii-500 after normal test returned 3000-3100mAh on those 4 batteries that were tested.

My Thinkpad’s battery that came with Sanyo cells have degraded over time and now takes about 40% of initial charge, those that got batteries with Panasonic cells never experienced such high degradation rate in similar periods of time.