Navigating with a constant GPS connection uses a lot of energy. There is no way to change this but there are some tricks to save battery on a long Tour:
The display uses a lot of energy – turn it off and use voice navigation so you don’t need to check the map. On your Android device, you can also use the function “Wake up screen.” Find it by tapping the loudspeaker symbol while navigation is running.
Turn off synchronizing for unused services, so they won't keep updating
Using your phone and listening to music eats up energy as well, as does using other apps simultaneously
A powerbank can be used to recharge your battery several times, and thus make sure you have enough battery until you reach the next plug.
On your Android device, turn off Wifi, so your mobile phone stops searching for it, deactivate mobile data, only use GSM or switch to flight mode entirely. Only your GPS remains activated. This is not recommended for Android though and impossible for iOS devices as Apple uses WiFi to determine your location.