Battery life for a bike phone uses as GPS is a problem. If you want to use your primary phone as your trip tracker, fine. As long as it's in your pocket running it's GPS app with the screen off it should be fine for hours.

If you want to have the phone mounted on the handlebars so you can see it, the solution is to have a second phone to use as a dedicated bike computer.

Older used Android phones are CHEAP. And plentiful.

Find one with a good sized battery, half decent screen, and a working GPS and you're set.

The screen on any phone takes up the vast majority of battery use. Nothing you can do about that as you need it on and at full brightness.

But other battery hogs are things like the cell radio. If you have a dedicated bike phone that doesn't need an active internet connection (load the maps at home on Wifi) you can put the phone in airplane mode and it's a huge battery saver. GPS is a passive listening antenna, not a broadcast antenna. It works fine in airplane mode.

Samsung makes an 'active' version of the Galaxy S series phones that are great for this because they are fully waterproof and more resistant to bumps and drops. Perfect for something that might get caught in the rain or knocked off the handlebars. You can get a 3 year old one affordably. If you're not really worried about waterproofing, you have so many good options for a cheap used Android phone it's insane.

You can also improve battery life on a bike phone by having the screen go off after 15 seconds. The catch on this is that you need to have a phone with a tap to wake feature where you can tap the screen and have it come on. When you're riding, tapping the screen isn't a big deal. Finding the power button on the side can be a hassle.

You can also strip the phone down to it's core needs. You can disable of freeze all kinds of stuff like most of the google apps that run in the background. You can get rid of the battery guzzeling Facebook app. Disable settings like syncing and calendars and all sots of stuff like that you will never need on a bike phone. Makes the phoen run really streamlined and efficiently.

I leave my screen on. But in airplane mode just running GPS with a 3500 mAh battery with most of the apps needed to make a phone as phone disabled. I can get a 4 hour ride in no problem. If I didn't keep the screen on I'm sure I could get 7-8 hours out of it.