Lithium-Ion-Poli can rest completely empty without problem, best and recommended level for longer resting is 40% of charge at 25C.
Li rechargeable batteries should made few full cycles on start of their lives to get full capacity, after then you can use it.
They have about 500-800 cycles before they die. Every day scientist working on some newer combinations and tech for this batteries to prolong life, decrease price, increase capacity, decrease charging time, increase security,...
But your constatation is completelly sure for Lead Acid batteries, maybe you mix them. ;-)