Testing new Eneloop AA batteries
I recently opened a new pack of “AA” size NiMH eneloop battery pack, based on the manufacturing date the batteries should be around 10 months old, so I thought that its a good idea to test the LSD NiMH (low self discharge batteries) claim made by Sanyo Eneloop batteries, these batteries capacity is rated at 2000 mAh when fully charged. The manufacturer claims that these LSD NiMH batteries should hold 90% of their capacity after 6 months and 85% capacity after 1 year of storage.
The first thing I did was to check the terminal voltage with my multimeter, it was 1.29v which sound fine as the batteries were 10 months old, also do note that these batteries are not fully charged by the manufacturer when they leave the factory, so its a fair guess based on the 1.29v that the capacity of the battery should be around 70-75% compared to full capacity.
Now I wanted to check the actual capacity left on the battery, for this I loaded the batteries on my La Crosse BC charger and set the mode of the charger to discharge mode, this would discharge the batteries and let me know the real capacity that this eneloop had in mA, the discharge process took around five and a half hours and the rated capacity for the two cells came to 1372 mA and 1385 mA which are some pretty decent figures which is close of 70% of full charge as the batteries are not fully charged when they leave the factory, so the Low Self discharge (LSD) feature works, as a normal NiMH rechargeable battery would have been completely self discharged if kept on shelf for 10 months.
Thereafter I did a full charge to these batteries and it took around 4 odd hrs to charge, I had set charging current was set at 500 mAh on the charger, the capacity of the two batteries came out a 2058 and 2106 mAh which is again very good because a normal NiMH batteries would require about 4-5 cycles to get to full capacity, you might have also noticed that these eneloops which are rated for 2000mAh were holding around 2100 mAh when they are fully charged, actually a fully charged eneloop measures around 5% more that its rated capacity.
The other interesting thing that I found out about the self-discharge rate of eneloop (and other LSD cells in general) is that the discharge rate is not linear, it loses a lot less capacity as the time goes by, for example an fully charged eneloop might lose upto 10% of it’s initial capacity during the first month of storage but it will lose just around 2-3% in the second month and this discharge rate slows even more after three months.
Needless to say I am impressed by eneloop batteries with their Low self discharge characteristics I recommend that if you are buying new NiMH batteries go with the LSD NiMH batteries like eneloops, I have seen eneloops to hold around 75% of their charge after 2 years of storage!
Another interesting thing about eneloop cells is that they have low internal resistance compared to regular NiMH cells and perform much better with loads so if your high drain devices like digital camera are showing poor performance with regular NiMH rechargeable cells give eneloop NiMH batteries a try, these batteries also perform much better in cold environment, also Sanyo claims that eneloop batteries can be charged almost 1000 times compared to regular NiMH batteries that are good for around 500 charge cycles.