British battery maker Ever Ready is patenting an idea for making small batteries child-proof. Batteries no bigger than buttons are just the right size for children to swallow but contain poisonous chemicals such as zinc and mercury.
Ever Ready plans to douse these batteries in a solution of denatonium benzoate, an intensely bitter chemical that is sold under the trade name Bitrex. The batteries are then heated in air to 120°C for four or five minutes. The chemical hardens as a surface coating, like sugar round a sweet.