Here is a guide to replace batteries in a Chatterbox Isolation unit. For Health and safety Reasons these actions should be conducted by a Professional Electrician, Also Noted that the Chatterbox Unit is a safety unit to prevent an explosion in an environment where Natural Gas/LPG or other Extremely Flammable Gases is present. We recommend Isolating the environment from the gas supply before work is carried out.   

Please find guide attached.