B737-900 Flight Attendant reported notifying Captain during taxi of passenger prohibited Lithium battery items in checked bag. Flight returned to gate where passenger retrieved items; returned to passenger cabin and flight departed safely.

Narrative

After the safety demo; Name of seat X came up to inform me that she has her laptop and camera in her check bag. That they contain lithium-ion batteries and there are also a spare in a case.I informed the [Flight Attendant] D of the situation and notified the pilots of the prohibited item.We confirmed the content of the bag with the guest and verify there was a spare lithium-ion battery and several electronic devices in the bag.We had no detail information on the battery or the status of the electronic device such as if it's properly turned off or properly packed.We returned to gate and the CSA (Customer Service Agent) had the guest remove her laptop and spare battery out of the bag. She decided to put her camera back into the check bag. FA D observed guest doing so and verbally asked if the camera is properly pack and turned off. She confirmed it was turned off.Guest returned to the plane with her laptop and battery.Interrupted sterile flight deck to inform pilots of prohibited item in cargo compartment (uninstalled lithium-ion battery and potentially improperly packed electronic with lithium-ion battery).