Increased (x4) battery consumption after initial period

I am getting a weird behavior with a navigation app I am developing. After more or less fixed amount of time (initial period) running in background in which the consumption was P percents per hour, the battery consumption increases drastically - same P percents are now consumed every 15 minutes versus every hour or so during the initial period.

I am able to reproduce this behavior on various devices ranging from iPhone 6 to iPhone X running different iOS versions with a bare simple app that can be simplified to:

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
  [self startLocationUpdates];
  return YES;
}

- (void)startLocationUpdates {
  self.locationManager = [[CLLocationManager alloc] init];
  [self.locationManager requestAlwaysAuthorization];
  self.locationManager.delegate = self;
 
  self.locationManager.desiredAccuracy = kCLLocationAccuracyBestForNavigation; //kCLLocationAccuracyThreeKilometers;;
  self.locationManager.distanceFilter = kCLDistanceFilterNone; //1000.0f;
  self.locationManager.pausesLocationUpdatesAutomatically = NO;
  self.locationManager.activityType = CLActivityTypeAutomotiveNavigation;
  self.locationManager.allowsBackgroundLocationUpdates = YES;
  [self.locationManager startUpdatingLocation];
}

- (void)locationManager:(CLLocationManager *)manager didUpdateLocations:(NSArray *)locations {
  self.lastLocationUpdateTimestampLabel.text = [self.dateFormatter stringFromDate:[NSDate date]];
}

I am getting the following results from the tests I conducted:

with location settings configured to max precision: 1% during the first 45-80 minutes (initial period), then 1% every 15 minutes

with location settings configured to lowest precision: 1% during the first 3-5 hours (initial period), then 1% every 40-50 minutes

Reseting RAM (as described in various places on the internet) reverts the behaviors to the starting point (regular consumption during the initial period).

Did anyone encountered similar battery consumption pattern when using location updates? Maybe during some other activity?