How to change batteries in your Oticon Opn invisible in-the-canal hearing aids

WARNING
New and used button/coin batteries are hazardous and should be kept away from children. Button/coin batteries can cause serious injuries if swallowed or placed inside any part of the body. Seek medical attention immediately if this is suspected.  The Australian Poisons Information Centre can be contacted 24/7 on 13 26 11 for fast, expert advice.