Hi, Peter!
I had the same problem - but that was 10 or more years ago! I sent in my transmitter to the MPX-service and they changed the buffer batteries. But the also changed some other things - I don't remember which today.
The best way ist to phone the MULTIPLEX Service! So they almost immediately can say what is the best way. They can also instantly say whether a new dispay is necessary and available.
Best wishes
profimc