Does using a navigation app affect GPS battery life on a hike?

The short answer

Having a navigation app open at the same time as a background GPS tracker does draw more battery, but not because two apps are competing for two GPS receivers. There is only one location subsystem on the phone, and any app with permission can receive updates from it. The extra cost comes from what a navigation app does on top of that fix — keeping the screen lit, redrawing a map, recalculating a route — not from the position fix itself.

What actually happens when two apps both want your location

iOS does not spin up a separate GPS receiver for every app that asks for one. A single location subsystem produces position updates, and any app that has been granted permission subscribes to that same stream. A tracking app recording a route and a navigation app giving directions can both be receiving fixes at the same moment without either one causing the hardware to work twice as hard to produce them. The receiver itself does not know or care how many apps are listening.

Where the extra battery drain really comes from

A navigation app giving turn-by-turn directions keeps the screen on for as long as it is in front of you, redraws the map continuously as you move, and recalculates a route whenever you drift from it. The screen is the single largest power draw on a phone in almost any situation, and a navigation app is built around keeping it lit and active the entire time it is in use. None of that is a GPS cost — it is a screen-and-rendering cost that would exist even if the phone only had one location-using app installed.

Set a route recorder running in the background and it does none of that. It keeps receiving position fixes with no screen required, at a modest and continuous rate, the same as it would if no other app were open at all.

Why a background tracker barely notices a navigation app in front of it

A GPS route recorder running in the background does not slow down, pause, or start working harder because a navigation app has taken over the screen. The two apps are drawing from the same location subsystem, not competing over it, so one being active in the foreground does not degrade what the other is receiving in the background. Whatever battery the tracker was already spending on a walk with no navigation app open, it keeps spending roughly that same amount whether or not a maps app is also running.

The one case where it genuinely adds up

The exception is not about conflict between the two apps — it is simple addition. A navigation app kept open and actively guiding for an entire long ride, rather than for the few minutes it takes to find a trailhead, spends its screen-heavy cost for that whole stretch, on top of whatever the background tracker was already spending. That is two real costs stacked on the same battery, not one cost multiplied by two. Close the navigation app once you have found the trailhead, or once you know the way, and its share of the drain stops immediately — the tracker underneath was never part of that bill in the first place.

Things that trip people up

• Assuming two location-using apps mean two GPS receivers running — there is one location subsystem on the phone, shared by every app that has permission to use it.
• Force quitting a navigation app to try to save the tracker's battery — this does nothing for the recorder, since the two were never sharing a workload to begin with, and it risks accidentally swiping away the wrong app in the switcher.
• Blaming a fast drain on "GPS being used twice" when the real cause is a screen kept on and a map being redrawn continuously — the same cost a navigation app would carry with no tracker running at all.
• Expecting the drain to stay high after the navigation app is closed — the screen-and-rendering cost stops the moment that app is no longer active, leaving only the modest, steady cost of the background track.

Where TrailCam fits in

TrailCam keeps recording a route in the background whether the screen is off or another app, including a navigation app, is in the foreground. Opening a maps app to find a trailhead, or to navigate the drive there, does not pause the track, does not need TrailCam to be closed first, and does not compete with it for GPS — the route keeps recording underneath at the same steady rate the whole time. TrailCam is free to download.