Is there some way to keep navigation from gobbling battery?

I have a new iPhone 12 mini and Watch 7 cellular. I've been doing a great deal of walking and using the pair for navigation, both with Apple and Google Maps. After about 6 miles (2-3 hours casual walking with stops) the phone has lost around 80% of battery life. I hand navigation off to the watch, but both watch map apps fail to remain open for more than a few minutes, making them pretty much useless. By the time I've gone a quarter-mile the home screen faces me when I look at my wrist. The phone carries the load and the maps are a huge battery drain on it.

Is there some way to cause the watch to either carry the full load of navigation or remain open while I click off the phone screen? I assume the screen is the major drain. What good is watch navigation if the device returns to the home screen so quickly? I've found no way to prevent the watch from doing that, so I can't see that it affords any value added to just using the phone. What am I missing?