Sorry foxtrotter,
I had to replace the battery on my tomtom 520t about 18 months ago.
Followed instructions off of the web.
Was pretty straight forward, however I am an avionics technician and had the use of a avionics workshop.
There was one part that was a pain, the battery is stuck to the back of the main printed circuit board with some incredibly strong glue, the use of plastic spatulas etc, a little (very little) use of a heat gun, you can prise it off.
But perseverance pays off eventually!
Ken