How to get battery level with 1 % accuracy .

       [UIDevice currentDevice].batteryLevel

Will give battery level with accuracy of 5%. But i recently used Battery Doctor App on my iphone 4S running ios 5.1, which is giving battery level with 1% accuracy . Anyone has any idea , how can we get that accuracy ... I have tried and searched a lot but not getting how they are calculating it .. Thanks in advance...

ios battery
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