You are keeping it in the garage and it is not fuel. If you are really concerned, remove the battery and store it in an ammo can (available from the local army surplus store). Don't store the battery in the house. It has nothing to do with temperature or humidity, but the potential for LiPo batteries to cause fires.

Something has to happen to the battery to cause a fire, and if it is not giving any symptoms (puffing or heating up) then it is ok. But, again, if you are concerned, store it separately and in something that is fire-proof such as a surplus ammo can... or a small concrete bunker..

CGr.