Lithium ion batteries are not inherently safe, but they are safer than many people may think. The Lithium-Ion battery contains no metallic lithium, which would be extremely reactive with almost anything. Side reactions can lead to a production of metallic lithium on the electrodes. Normally these side reactions are so small and slow that the produced lithium reacts instantly and increases the SEI (see above), which is an essential part of the cell anyway. Certain circumstances however, can lead to accelerated side reactions. For example overheating, over-voltage or penetration. A battery management system and proper mounting in a suitable location can avoid these situations. All lithium ion batteries in portable devices make use of safety circuits or battery management systems. Most manufacturers perform safety tests with their batteries, such as nail penetration, crash tests, short circuiting, overcharging and overheating.