The biggest threat to Lithium-ion batteries is thermal runaway. Thermal runaway of the lithium-ion battery initiates an unstoppable chain reaction. The temperature rises rapidly within milliseconds and the energy stored in the battery is suddenly released.

Several factors can lead to thermal runaway of a lithium-ion battery:

• Internal short circuit: Due to an accident or similar mechanical impact, e.g. if a tool falls down from a great height, the battery is deformed, material penetrates the battery cell and triggers an internal short circuit.

• External short circuit: Deformation of the battery cell causes an external short circuit.

• Overcharging the battery beyond the maximum voltage specified in the data sheet. Depending on the degree of overcharging, the battery may be damaged permanently and the service life of the battery decreases.

• Overheating/Excessive currents when charging. Recharging a Li-ion battery will cause the temperature of the battery to increase.