In general, Lithium ion batteries (Li-ion) should not be stored for longer periods of time, either uncharged or fully charged. The best storage method, as determined by extensive experimentation, is to store them at a low temperature, not below 0°C, at 40% to 50% capacity. Storage at 5°C to 10°C is optimal. Since lithium batteries self-discharge, it is recommended that they must be recharged every 12 months.
