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    <p>It's usually considered best practice to avoid polling and instead ask for notifications from the system, like so:</p> <pre><code>[[UIDevice currentDevice] setBatteryMonitoringEnabled:YES]; [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(batteryLevelUpdate) name:UIDeviceBatteryLevelDidChangeNotification object:nil]; </code></pre> <p>…where the <code>batteryLevelUpdate</code> would look like this:</p> <pre><code>- (void)batteryLevelUpdate:(NSNotification *)notification { // do whatever, using: [[UIDevice currentDevice] batteryLevel] } </code></pre> <p>From the <a href="http://developer.apple.com/library/ios/#documentation/UIKit/Reference/UIDevice_Class/Reference/UIDevice.html#//apple_ref/doc/uid/TP40006902-CH3-SW20">UIDevice Class Reference</a>:</p> <blockquote> <p>Notifications for battery level change are sent no more frequently than once per minute. Do not attempt to calculate battery drainage rate or battery time remaining; drainage rate can change frequently depending on built-in applications as well as your application.</p> </blockquote> <p>Once per minute is 10x more often than your code is currently checking while exerting much less effort CPU-wise. It does <em>not</em> mention, however what granularity of changes will cause notifications -- is a 0.01% change going to send, or does it require >1% change?</p> <p>To answer your other question if you should set the <code>setBatteryMonitoringEnabled</code> back to <code>NO</code> : if you are using the notifications and not manually polling for batteryStatus then the answer is that you must leave it at <code>YES</code>, or risk missing the notifications.</p> <p><a href="http://developer.apple.com/library/ios/#samplecode/BatteryStatus/Introduction/Intro.html#//apple_ref/doc/uid/DTS40008812-Intro-DontLinkElementID_2">Apple's official BatteryStatus Sample Code</a> uses this same take on a battery-status reporting.</p> <p>There is also a <code>UIDeviceBatteryStateDidChangeNotification</code> which will notify you when a device is discharging (in use), charging or has become fully charged.</p>
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