I was struggling a bit, so pulled off the sticker strip at the bottom and found the 2 screws mentioned by others.

Then I followed this excellent guide. Purchased recommended replacement battery.

This ‘ancient navigator’ is back in operation, and suits me weill i.e. it’s cost just the battery.

TomTom kindly offered a replacement for only about $300 [for what I recall cost about $80 years ago], but I decided that I’m happy with my ‘ancient navigator’,

and spending the money on other things … And they’ve updated the map etc (for the last time of course) for free.

Lovely to have this ‘antique’ back in operation. Big thanks to Ifixit and Sean.