Tons of variables here. I leave the stand alone gps home for on the road tours, but might take it for off road tours. I manage to do that mostly thru minimal phone usage.
Battery issues vary with the phone and how you use it as well as how and where you tour.
Phones with replaceable batteries and extra batteries are a big plus IMO. The batteries don't weigh much and can be bought fairly cheaply if you don't buy them from the company that sells the phone.
Batteries last pretty well if you turn off most of the phones functions except the GPS. They last forever if you turn the phone off. How complicated is your route? Often mine is pretty simple most days. I know people who can look at even a complex route in the morning and remember it all day.
I use the phone pretty sparingly when away from power. If I want to check in with home a quick text is enough. No need to ever take incoming calls. Checking texts and emails one a day is plenty.
Power wallets can extend battery range as can various charging methods. I can generally go a long time between charging due to all of the above. If that is not the case for you a GPS that takes replaceable batteries is one easy solution since you can carry as many aaa batteries as you want.