Battery drain after Android 6.0 update using factory image flashing on Nexus 7 2013

I am seen huge battery drain on Nexus 7 2013 after flashing Android 6.0 factory image. Even battery usage option screen gives strange result. For example -- Total battery % used by all the apps just show 9%, while total battery left is only 73% after fully charging of 100%. So where is the remaining battery of 18% gone, which is not even showing up in battery uses option screen?

Attached herewith is screenshot of battery usage screen. And I really notice huge battery drain with Android 6.0 as compared to earlier Android 5.1.1.

Please help and let me know.

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