Save battery power between charges with the battery saver. When you switch this on, the app runs in the background, and you’ll hear navigation instructions when being guided along a route. In other cases the GPS will be switched off to reduce power consumption.”Now the Finns are updating their Nokia Drive+ Beta application with a power saving mode, or, in Nokia's words: "
There are also the usual bug smashes and stability improvements, so the WP8 Nokia Drive should behave much better after the update. Happy now?
source: Nokia Drive+ Beta (WP Store)