iPhone GPS - Battery Draining Extremely Fast

Question

We are developing an app that has heavy GPS usage, and we are unable to optimize the battery life.

Even when the device is not moved, there is significant battery drainage that, according to the code, should not happen.

Here is the code:

locationManager = [[CLLocationManager alloc] init];
locationManager.distanceFilter = 100;
locationManager.desiredAccuracy = kCLLocationAccuracyHundredMeters;
[locationManager startUpdatingLocation];

Ideally we want to trigger GPS every 20 minutes (if there is no location change then save battery) OR every 5 minutes if there is location change. According to my developer this cannot be done

Previously we were using kCLLocationAccuracyBest, which was consuming battery very fast and now we are using kCLLocationAccuracyHundredMeters.

startUpdatingLocation - is to get the GPS coordinates. There is another call startMonitoringSignificantLocationChanges which is to get AGPS coordinates which I believe returns the coordinates whenever cell tower will change, and hence consumes battery really fast.

distanceFilter - The minimum distance (measured in meters) a device must move laterally before an update event is generated. On the basis of distance filter we get the GPS fix from the device and then we send the updated GPS coordinates to the server.

Any help will be greatly appreciated Thank you!

Answer 1

Ideally we want to trigger GPS every 20 minutes (if there is no location change then save battery) OR every 5 minutes if there is location change. According to my developer this cannot be done

This could be done using an NSTimer that calls a startLocating (a custom method that creates the CLLocationManager and calls startLocating on it) method every 20 minutes. Make sure you call CLLocationManager's stopLocating once you've found a CLLocation with an accuracy of your liking.

However, doing so mean that for 20 minutes you might be using a location that is totally off. It depends on how you plan to use the location and how precise it needs to be, but maybe what your dev means by "not possible" is that your app needs the user's actual location at all times.

Answer 2

There is another call startMonitoringSignificantLocationChanges which is to get AGPS coordinates which I believe returns the coordinates whenever cell tower will change, and hence consumes battery really fast.

That's exactly what it does, but you're jumping to conclusions about the power required for that. The GPS receiver and WiFi transceiver can be used to help determine location, but they're extra devices that have to be powered to be useful. But mobile phones like the iPhone need to keep in touch with the nearest cell tower anyway in order to receive phone calls, so using cell towers as a source of location information should be very efficient with respect to power. Here's what the CLLocationManager reference page says about -startMonitoringSignificantLocationChanges:

This interface delivers new events only when it detects changes to the device’s associated cell towers, resulting in less frequent updates and significantly lower power usage.

It also describes the service as providing "tremendous power savings," so it seems the right tool for the job you describe. Of course, if you're also using the standard location updating mechanism at the same time you won't see that power savings, so make sure you're not using both.

Ideally we want to trigger GPS every 20 minutes (if there is no location change then save battery) OR every 5 minutes if there is location change. According to my developer this cannot be done

It sounds like there's some sort of misunderstanding here. You can certainly fire up the GPS every 20 minutes to get a fix if that's what you want, although you can't do that from the background. The significant location change service will notify your app even if it's running in the background, so perhaps your developer is talking about background updates.

Answer 3

If you require a good level of precision, you should startUpdatingLocation and as soon you get the first fix you should then stopUpdatingLocation and then startMonitoringSignificantLocationChanges.

This is enough for most app purposes.

Answer 4

Your belief that startMonitoringSignificantLocationChanges consumes the battery really fast is likely incorrect. Cell tower changes usually occur far less frequently than movements of 100 meters. And an iPhone checks for this event even when idle and all apps are sleeping.

However, keeping a cell phone on (e.g. Airplane mode off) when far from any tower (barely 1 bar) will drain the battery of the device whether or not an app is doing any location monitoring.

On stock iOS devices, an app cannot trigger location monitoring purely on a timer basis such every 20 minutes or every 5 minutes, without keeping the device on and your app running in the foreground, which will drain the battery.