Storing your drone batteries when not in use is one of the most important steps to ensure the safety of the batteries themselves, yourself, the people around you, and the drone itself.
While batteries found in most consumer level drones, specifically from brands such as DJI and Autel Robotics are safe there is always a chance something could go wrong and result in a fire.
Discharge your batteries
The easiest and something you might already be doing without even realising is putting the batteries into discharge mode. It's better to have a battery with almost no energy in it compared to one full of energy.
DJI's latest drones already do this if the battery hasn't been used for a certain amount of time. As for other drones, if a companion app is used there is often a switch that can be turned on to put the battery into discharge mode.
For drones that don't use an app, some battery chargers can discharge batteries when turned to discharge mode. If none of the above applies you can run the battery to empty by flying the drone.
Use a battery safe bag
An added layer of protection is using a battery safe bag or compartment. Battery safe bags are usually fireproof pouches that allow you to store multiple batteries inside. In the event of a fire, it will be contained in the bag and prevents it from spreading further.