I have had my Swytch bike for two years , no problems at all. I have an old and new style battery on the bike. but changing leads is somewhat "fiddly" to get all the little pins lined up correctly. Could you invent two Y junctions so that both batteries are connected . This is what I mean. The tail of Y ONE connects to the power lead on the wheel, one of the "arms" to one battery the other to the other battery. The tail of Y TWO connects to the magnet on the chain wheel, one arm to one battery, the other arm to the other battery. This means that only one battery will be switched on at a time, when that goes flat, press off button and press on button on charged battery