1,电池级别和电池状态监听通知
[[UIDevice currentDevice] setBatteryMonitoringEnabled:YES];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(checkBattery:) name:UIDeviceBatteryStateDidChangeNotification object:nil];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(checkBattery:) name:UIDeviceBatteryLevelDidChangeNotification object:nil];

2,电池的四种状态：
NSArray *stateArray = [NSArray arrayWithObjects: @"Battery state is Unknown", @"Battery is not plugged into a charging source", @"Battery is charging", @"Battery state is full", nil];

 3，[[UIDevice currentDevice] batteryLevel] * 100];//电池的级别，一般都是0.0--1.0之间；

[[UIDevice currentDevice] batteryState]；//电池的状态

完整代码：

- (void) doLog: (NSString *) formatstring, ...
{
    va_list arglist;
    if (!formatstring) return;
    va_start(arglist, formatstring);
    NSString *outstring = [[[NSString alloc] initWithFormat:formatstring arguments:arglist] autorelease];
    va_end(arglist);
    [self.log appendString:outstring];
    [self.log appendString:@"\n"];
    self.textView.text = self.log;
}

- (void) checkBattery: (id) sender
{
    NSArray *stateArray = [NSArray arrayWithObjects: @"Battery state is Unknown", @"Battery is not plugged into a charging source", @"Battery is charging", @"Battery state is full", nil];
    self.log = [NSMutableString string];
    [self doLog:@"Battery level: %0.2f%", [[UIDevice currentDevice] batteryLevel] * 100];
    [self doLog:@"Battery state: %@", [stateArray objectAtIndex:[[UIDevice currentDevice] batteryState]]];
}

- (void) viewDidLoad
{
    self.navigationController.navigationBar.tintColor = COOKBOOK_PURPLE_COLOR;

    // Enable battery monitoring
    [[UIDevice currentDevice] setBatteryMonitoringEnabled:YES];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(checkBattery:) name:UIDeviceBatteryStateDidChangeNotification object:nil];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(checkBattery:) name:UIDeviceBatteryLevelDidChangeNotification object:nil];

    // Keep checking
    [NSTimer scheduledTimerWithTimeInterval:0.1f target:self selector:@selector(checkBattery:) userInfo:nil repeats:YES];
}