Tournedos - many thanks for your advice.  I followed your instructions and I'm delighted to say they worked.  The radio will have to be retuned but everything else is operational.  Thank you again.

Kind regards.

That's great to hear! It will need to be repaired properly some day, but after this result it is safe to say the problem is just the battery. It won't be too expensive once you find someone willing and able to do the job, and this system is definitely worth keeping in use.