The mapping can be very expensive depending on what you want - however, once you have it you'll never need to buy another map (OK footpaths get diverted etc)
I have the Platinum cards for both North and South of the UK and they cover every part of the country at 3 scales
1:10,000 (1mm on the screen is only 10 metres 'on the ground'
1:25,000
1:50,000
You can zoom in on each of those (although the detail is still that at the original scale) you can have, for example the 1:25,000 zoomed in to 1:11:000 or the 1:10,000 zoomed into 1:2,000
Streetview at 1:10,000 shows individual houses, gardens etc.
You can adjust the power usage by having it update every 10 seconds, or 30 seconds instead of every second - how far do we walk every 10 seconds ? Do we need an update ?
My battery lasts about 16 hours (2 days at 8 hours)