QUOTE from Eneloop FAQ:
Should I store my batteries charged or uncharged?
If stored with charge, it is possible that when you return to use the battery there may still be some charge left in the battery, therefore it will enable you to use it right then and there. Also, by keeping some charge in the battery, it will require you to "cycle" the battery fewer times until it reaches its peak charge. If you store them with no charge, you will have to "cycle" the battery multiple times until it reaches its peak charge.
http://www.eneloop.info/home/faq/eneloop.html