Storage units are generally considered to be safe places in which you can keep your items. However, not all items should be kept in long-term storage. So, what are some items you should not store long term, and what can happen to them if you decide to do this?
Corrosive or dangerous materials
Those kinds of items not only lose their properties as time passes, but they also can pose a significant danger to your other items and potentially be a danger to the whole storage facility. Most storage facilities won’t even let people store those items.
Corrosive and dangerous items are fuel, chemicals like pesticides, propane tanks, firearms and ammo, explosives, alcohol and liquor, and even batteries. Batteries can corrode over time and damage nearby items. When the setup is just “right” they can even explode or catch flames. But the most common way batteries can damage items is when they are inside electronics for a long time.

One of the most common problems in long-term storage units is caused by batteries. This is why batteries are certainly among the items you should not store long term.
Also, make sure to drain any motors and other machines that use fuel and oil before storing. Keep your storage unit safe, not only for you but for every unit owner in the facility.
Illegal items
This should come as no surprise, but illegal items don’t go only against the law, but they can potentially be dangerous. Also, you and the storage facility can get in legal trouble for those items. Those are illegal drugs and opioids, illegal weapons, and many other things.
Expensive or important artwork
Even the best climate-controlled storage units cannot fully protect od and fragile artwork. Of course, if you are sure that your art is going to be safe inside of storage unit, feel free to keep them there. However, make sure to use climate-controlled storage.
Paintings and antiques can especially be sensitive to fluctuations in humidity and temperature, as they can easily disfigure, bend, catch mold, and warp. Also, you can irreparably damage antiques with mechanisms, like old clocks, if you don’t keep them properly.
So, if you have to keep them in storage, make sure to have a unit with climate control. Otherwise, don’t keep them there under any circumstances. Also, make sure that the storage is safe if you want to keep your valuables inside and that it has good security systems.

Expensive or family artwork is certainly one of the items you should not store long term in a storage unit
Stuff that requires regular maintenance
You shouldn’t keep complex machines and mechanisms that you need to regularly check and maintain. You’ll need to visit those items regularly, and many of them can be irreparably damaged if they are left without proper supervision.
Documents and files
Sure, you can keep documents and files in storage, but you shouldn’t keep important ones in a storage unit. The nature of those documents can vary. From documents that prove your identity to medical documents and documents that are important for your job. Those are certainly some of the most important items you should not store long term.