Are solid-state batteries safe? The Battery Nail Penetration Test will tell you the answer. Put the fully charged battery on a flat surface, and use a steel needle to pierce the battery radially, which is to test whether the battery catches fire or explodes. In daily use, the battery may be short-circuited due to being penetrated by foreign objects. So the test can well reflect the occurrence of battery short circuits. When the steel needle penetrates, the steel needle provides a short-circuit path inside the battery, and the electric energy of the battery is converted into heat energy and stored inside the battery. The short circuit causes the concentrated explosion and release of energy in a short period, which may cause smoke and leakage. Even catch fire and explode.