How reliable are these batteries? Can the batteries overheat and cause fire?

Bosch has tested all of these aspects during development, and now more than 10,000,000 of its power tools with lithium-ion technology are being used in all manner of conditions with no problems. It is a well-known fact that heat emerges within batteries. The specifically developed red ribs on the battery are used for heat dissipation, and the chargers feature a built-in fan for further cooling of the battery.

They also have additional temperature sensors that terminate the charging process if a fault is detected.