iPhone battery use

I am using CE on my iPhone for tracking outings by dingy away from the main boat. This requires operating on the iPhone battery. A couple hours of tracking uses most of the battery life. Is there a technique to reduce battery use while tracking?

I don’t have a solution to reduce battery drain, but I use a Makita tool battery and adapter to charge the phone. Makita makes a slide on adapter that provides 2 usb ports

I am all set for recharging my phone, but I don’t want to do that out in my dingy. Using Coastal Explorer on my iPhone away from the main boat I want to extend battery life.