Frog: I went to our true expert on the subject; JJ Hong, Pres Kokam Engrg Ltd and here is his answer: The cathode material is lithium cobalt oxide. When you apply charge current, the ionized lithium from the cathode will move to the anode. If excessive lithium ions move from the lithium cobalt oxide structure for a long time, the the structure might be damaged due to the excessive absent of lithium ion. That's why we recommand that you do not store the lithium at full charge state. Rather, less than 80% is good if you store the battery more than 6 months.