This is from Page 14 of the battery owner's manual:
For Lithium-Ion battery pack storage longer than 30 days:
Store the Lithium-Ion battery pack where the temperature is below 80°F (26°C) and
free of moisture.
Store Lithium-Ion battery packs in a 30%-50% charged condition.
Every six months of storage, fully charge the Lithium-Ion battery pack.
Exterior may be cleaned with a cloth or soft non-metallic brush.
NOTICE: This battery pack has equipped with an advanced self-maintenance
function. It can maintain 30% of its charge capacity automatically after it is stored
over one month.