Showing your age
The KXT308 dates from late 1980's whereas the KX-TEA308 came out around 2005. The backup battery on KX-TEA308 that I was asking about is the button cell soldered in - as in the Farnell link.
Was the thought that the more modern systems wouldn't be around beyond the life of the battery?
You've only got to look at how a Raspberry Pi - little bigger than a box of long matches - can handle more lines that a former GPO rural exchange and provide far more facilities ! My system has over 250 lines working off it that terminate in fifteen countries. How things change! To think that over 20% of the GPO's exchanges were still manual when I started out as one of 'God's Poor Orphans' all those years ago but luckily have kept up with technology. Commissioned the exchange that went straight from manual to electronic and senior commissioning engineer on the UK's first large electronic exchange in the early 1970's and now they've all long gone! Now I just have several ex-GPO exchanges ranging from small manual magneto and CBS manual ones through an early Strowger one from the 1920's to the
last step-by-step 'Strowger' system that survived in public service until July 1995 plus the VoIP Raspberry Pi system connected to the worldwide CNet (Collectors Network).