Can black substance inside the radio battery kill human?

The black substance found inside a radio battery is often a result of leakage or corrosion and can include toxic materials like potassium hydroxide or lead. While direct contact with this substance can be harmful, it is unlikely to be fatal unless ingested in significant quantities or if it causes severe chemical burns. However, exposure should be avoided, and proper safety precautions should be taken when handling damaged batteries. If there are concerns about exposure, it's best to seek medical advice.