If a passenger reports having spare lithium batteries in checked baggage, what action should cabin crew take?

When a passenger reports having spare lithium batteries in checked baggage, the appropriate action for cabin crew is to inform the pilot and complete any necessary forms. This action is critical because lithium batteries can pose a fire hazard if damaged or if they short-circuit, especially in the cargo hold of an aircraft. The pilot needs to be aware of potential safety risks, as they are responsible for the safety of the flight. Completing necessary forms ensures that the situation is documented properly, which is important for safety records and adherence to regulations governing the transport of hazardous materials.

The other options do not adequately address the safety concerns associated with lithium batteries. Allowing the passenger to keep the batteries does not mitigate the risk of fire or damage, while confiscating them without following proper protocol may lead to issues with the handling of hazardous materials. Advising the passenger to remove them, while it acknowledges the potential hazard, does not involve directly informing the flight crew, which is essential to ensure all safety measures are taken.