For navigation assistance from an android phone, I'd use the Osmand app. It will reroute should you get off track or desire a new course. Using its own database, you can place your phone in Airplane mode with screen off, listen to voice prompts,and ride a very long time with OSMAND before needing external power. Used with an Edge 500 or similar for map and metrics display, you'll be done in no time with that solo double century. If it's over 12 hours, no worries, you've got that two port external battery pack available for your phone and bike computer.