The study of battery external short-circuit (ESC) damage characteristics is of great significance for the design of high-reliability fusing protection. Based on the self-developed controllable ESC test platform with a minimum time of 0.1 ms and a maximum overcurrent of 5000 A, taking lithium-iron phosphate cylindrical lithium-ion batteries as the research object, ESC tests with different current and time combinations are carried out. The study proves that there are three damage modes in the ESC of lithium-iron phosphate batteries: rupture leakage, internal fusing and cumulative damage. The ESC safety, fusing and performance damage boundaries all have inverse time characteristics, and the first two boundaries have an intersection point at the RMS current value of 30C. If the current is less than the intersection value, it is easy to touch the safety boundary to cause rupture and leakage accidents, increasing the safety risk; if the current is greater than the intersection value, it is preferred to touch the fuse boundary and fuse protection will occur, and the protection reliability is improved. For batteries that have not fused or ruptured, there is a risk of cumulative failure from multiple ESC impacts. Based on the findings, full consideration of the ESC damage characteristics of a battery can ensure that the battery system does not produce excessive damage in the case of ESC and thereby improve system safety.