Got it sorted now.

The mug was indented at the bottom with a plastic piece in the indent.

I prised this off to find the battery and player attached to it.

I disconnected the battery and chucked the whole plastic piece in the rubbish bag

Even though I thought I had disconnected the battery, it was still playing as I dropped the bag down the chute.

Don`t know what the caretaker will make of it.