I got really fed up with my Nokia 1020 last week. The battery seemed to be getting worse. On one day, I was doing a 2 hour drive using the Here+ app to navigate. With the phone plugged in and charging from the car, the battery was still discharging and was down to about 5% when I got there. So I guess the GPS must consume more power than the car can provide.
On average with nothing switched on (blue tooth, wifi, GPS etc), the phone was discharging at about 8% per hour. I compared it to my Nokia 620 and it was discharging at about 1.76% per hour with everything turned on.
I chatted with Nokia again and we did a hard reset of the phone which basically wipes it and starts again and then restore all of the content and apps. I was a bit skeptical, but it does seem to have made a big difference. If I use it heavily, it still does discharge reasonably quickly, but at least when it is ‘at rest’ it seems a lot less power hungry.