Gadget_Guru
Newly Enlightened
Howdy all,
I bought a single unprotected "5000mAh" 25500 (C-size) Li-Ion (Cobalt) cell from Deal Extreme in September, 2008. Here is the page on DX's site.
At the time, I tested it with my Turnigy Accucell-6 charger. I charged at 2A to 4.20V, then discharged at 1A to 3.00V. The measured capacity was 2918mAh, not bad, but certainly no where near the rated 5000. This gross exaggeration of capacity is typical of cheap Li-Ion cells, in my experience.
So, lacking any immediate need for the cell, I used the Accucell charger's storage feature, and brought the cell to 3.8V, and put it on the shelf until I had need of it. There it sat at room temperature until I checked it a week or two ago. Cell voltage measured practically zero, and attempts to charge were unsuccesful.
Curious as to the cause of the failure, I peeled off the shrink wrap and insulating washer from the + end of the cell, and discovered this corrosion from leakage:
Has anyone else experienced similar failure with these cells?
I wonder if it's just a fluke bad cell. I have had good quality 18650 Li-Ion cells sit for YEARS in storage, with little loss of capacity, even when stored fully charged.
I bought a single unprotected "5000mAh" 25500 (C-size) Li-Ion (Cobalt) cell from Deal Extreme in September, 2008. Here is the page on DX's site.
At the time, I tested it with my Turnigy Accucell-6 charger. I charged at 2A to 4.20V, then discharged at 1A to 3.00V. The measured capacity was 2918mAh, not bad, but certainly no where near the rated 5000. This gross exaggeration of capacity is typical of cheap Li-Ion cells, in my experience.
So, lacking any immediate need for the cell, I used the Accucell charger's storage feature, and brought the cell to 3.8V, and put it on the shelf until I had need of it. There it sat at room temperature until I checked it a week or two ago. Cell voltage measured practically zero, and attempts to charge were unsuccesful.
Curious as to the cause of the failure, I peeled off the shrink wrap and insulating washer from the + end of the cell, and discovered this corrosion from leakage:
Has anyone else experienced similar failure with these cells?
I wonder if it's just a fluke bad cell. I have had good quality 18650 Li-Ion cells sit for YEARS in storage, with little loss of capacity, even when stored fully charged.
