iphone: Calculating battery life

Question

Wondering if there are references beyond the Apple tech stats for calculating battery life. I've tried comparing some existing battery apps (battery % left * Apple's figures) and I dont come up with the same answers sometimes. Also there are stats for using 2G cell (as opposed to 3G) and I dont see anything on Apple for 2G battery life.

Of course, some of the apps claim they are 'the most accurate'... but I dont see that happening unless someone has a source for very accurate stats.

Thanks

Answer 1

The API allows you to register to receive notifications for changes to the battery level. It only reports a change at 5% increments up or down, but you can use a timer and measure the time between two changes (or initial battery level and first change). Here's how you register for the notifications:

// Use this call to get the current battery level as a float
// [[UIDevice currentDevice] batteryLevel]

[[UIDevice currentDevice] setBatteryMonitoringEnabled:YES];

[[NSNotificationCenter defaultCenter] addObserver:self
                                         selector:@selector(batteryStateDidChange:)
                                             name:UIDeviceBatteryStateDidChangeNotification
                                           object:nil];

[[NSNotificationCenter defaultCenter] addObserver:self
                                         selector:@selector(batteryLevelDidChange:)
                                             name:UIDeviceBatteryLevelDidChangeNotification
                                           object:nil];

The first notification tells you the current state, e.g. unplugged, charging, or full. The second will get triggered whenever a 5% increment is reached.

Seems to me that if all you're given is change notifications at 5% changes up or down, accuracy is not something you can calculate very well or quickly. A 5% change could take a very long time if the device isn't doing anything.

Maybe you can monitor [[UIDevice currentDevice] batteryLevel] with a timer, however, while I haven't tried it I think it only gets updated at this same 5% increment.