I have been intrigued by the huge number of sellers of very low cost 18650 Li-ion cells on eBay.
Could they be any good?
As a reality check, Panasonic cells around 3000mAh sell through traditional channels here in Australia for around A$20 per cell, there are Australian eBay sellers selling cells advertised as Panasonic for around A$22 per pair posted.
The cells weighed around 35g, at the low end of the common range and probably quite low for 5300mAh. The cell length was 66mm (18650 cells are all over the place, and not just due to the sometimes included protection module).
Each cell was charged and discharged three times to ensure that it was exhibiting full capacity.
Above is a discharge curve for the 5 cells at 2.5A, 0.47C.
Four of the five cells showed less than 200mAh, less than 4% of rated capacity. One cell showed 900mAh, less than 17% of rated capacity.
One is amazed that so many are apparently sold, they cannot all be purchased by would be testers like myself, and it can’t be sustainable if everyone realised they were duped and obtained a refund.
By contrast, here is the published discharge characteristic of a Panasonic NCR18650 2750mAh Li-ion cell.
Note that discharge at 0.5C should deliver approximately the rated capacity of the cell.
Update: 10/01/2015. A request of the seller for full refund has been satisfied, though with some delay by the seller who sought to make a partial refund and guarantees of good feedback.
Since first writing this article, I found an interesting evaluation on eBay’s own site: 18650 Battery Buying Guide (test on all from eBay below $3).
I am now happier to pay A$22 for two Panasonic NCR18650 3400mAh cells posted from Melbourne, and have purchased some… but I will test them to be sure.