On Wed, 14 Oct 2020 11:07:24 +0100 (BST), "Dave Liquorice"
wrote:

snip

Yeah, this seems the simplest solution. Two bell units with batteries
fitted in both everything series connected. The gotcha might be
getting a second ding-dong unit that presents a similar load to the
orginal but it's probably not that critical.

Assuming they haven't changed the design in the last 30 years ... ;-)

https://www.tlc-direct.co.uk/Products/VE107.html

Alternatively, I could rewire one unit to be just the bell (takes me
back to my BT and 706 days g) and replace the batteries in the main
unit with 3 x 18650's. ;-)

Could do but you have to faff about making a holder for the
18650's...

Well, where it's fitted there is space behind (under the stairs) so it
could just be a hole though the back and a pack kept there.

However, finding space to mount and run wire to a second unit isn't
that easy, that's why I liked your mini mechanical buzzer idea (as
that could be mounted behind the bell push on the frame itself).

So maybe I could do both, find a suitable mechanical type buzzer and
up the voltage (giving more options on the buzzer), as at least that
would be easy in that I don't have to work out how I got the wire from
the bell to the push putton? ;-)

Cheers, T i m