Leaving Eneloops and other LSD cells sitting unused for months...

Black Rose

Flashlight Enthusiast
Joined
Mar 8, 2008
Messages
4,626
Location
Ottawa, ON, Canada
what are the risks?

I have a nice collection of Eneloops (44 AA, 12 AAA), some that are in actively used lights and radios, and I have 16 AAs that are designated as backup cells.

I figured that since the backup cells hadn't been used in approx. 6 months I'd discharge them (500 mA) and then perform a Refresh & Analyze on them with my C9000 (1000 mA charge/500 mA discharge).

Well this morning the second set of 4 completed the cycle, and I have two more Eneloops that are reporting in below the 1900 mAh nominal rating.

The latest two affected cells came in at 1884 and 1888 mAh. The previous one came in at 1870 mAh.
These cells came in at between 1951 and 1971 mAh when I performed the break-in on them when new.

I general I have noticed with the C9000 that the difference between the reported break-in capacities and regular charge capacities is about 90 - 100 mAh.
A good example from my own reporting is here.

The Eneloops are advertised as being able to hold 85% of their charge after 1 year, but what is the risk to the cells of leaving them sit around unused for 6+ months?

Also, is the 1900 mAh nominal capacity based on the IEC standard charge or a regular charge?
 
The industry standard for reporting the capacity of all NiMH batteries, including Eneloops, is based on the IEC standard charge. You can see the Eneloop AA data sheet here, which confirms that (see note 1 of the specifications).

According to Sanyo documents, Eneloops will last much better in storage (when stored charged) than other types of NiMH, but even so after six months or more they will start to develop a higher internal resistance. This higher internal resistance will cause voltage depression on discharge and an apparent reduction in capacity. This high resistance condition is temporary and can be reversed by one or more IEC standard charge/discharge cycles.

With my Eneloops I routinely notice capacities less than 1900 mAh if I charge them normally on the C9000 and do not give them a top off afterwards. This is more due to less complete charging than any problem with the cells.

I have also noticed that my 2006 vintage Eneloops seem to have an average capacity about 50-100 mAh lower than 2008 versions. I do not know if this is deterioration due to age, or if the cell design was improved in more recent production.
 
Most, if not all, my AA Eneloops come out in the 1800s on my Maha 9000. Some IIRC are in the 1700s. Age of them ranges from 6 mos to a year and receive regular use.
 
Top