I have been searching for a replacement electronic CH programmer that
does not depend on a battery for backup of the settings, planning
ahead for the time when I shall not be here.

I thought I had found what I need in the Drayton Invensys LP522
programmer. Their Product brochure states:

" Uniquely in the controls market, the Lifestyle range now has
automatic summer/winter time adjustment, making the bi-annual
summer/winter manual reset a thing of the past.
In addition, the LP range has a new, highly accurate, preset clock,
virtually eliminating the need for time adjustments through the
product’s life.

The new "memory saver" feature provides peace of mind for the
user, especially in the event of power interruptions or power cuts.
The time and programme memory are always saved..
LP users will never again need to search for their instructions to
remember how to re-set or re-programme the clock. "

Sounds ideal.

However, the Technical Details state that it has a lithium battery.
This probably has a life expectancy of 10 - 15 years maximum, so there
will come a time when it needs to be replaced, and whilst this can be
done ( http://west-penwith.org.uk/blog/archives/222 ) it looks a
tricky job for a non technical person.

Solid state non-volatile memory chips used in lots of domestic
appliances are cheap enough so I would hope that is how the settings
are stored, and it may be that the battery is there solely to maintain
the clock during power failure. The obvious solution here would be a
radio controlled clock (again very cheap nowadays) which would reset
itself on restoration of power.

Does anyone know of an alternative product that would meet my needs?
All the ones I have checked so far depend on a battery for backup.

The simplest solution I suppose is a programmer with an easily changed
battery and a scheduled annual replacement of battery, say along with
the smoke alarm battery change, but my existing programmer flattens
the battery in the event of a power cut lasting just a few hours, and
then it's back to re-entering all the settings.