Keith's 'I know I will get lost.....' reminds me of all the times I've taken a 'short cut' only to not know where the hell I am and take half an hour and several miles longer than I would have.
I use a Satnav when I'm on a long ride. I put the Satnav in my pocket and use earbuds to only listen to the guidance. This works pretty well until a road is closed and a diversion is in place. The darned Satnav constantly brings me back to the closed route! If I could view the map I could make my own choices.
To keep the device going long enough for the journey I plug it into a battery pack in my pocket.