NFC battery draining through constant use

The Tag Dispatch System of Android Developers says

Android-powered devices are usually looking for NFC tags when the screen is unlocked, unless NFC is disabled in the device's Settings menu. When an Android-powered device discovers an NFC tag, the desired behavior is to have the most appropriate activity handle the intent without asking the user what application to use.

Therefore, your device is scanning for NFC tags, when the screen is on , so power would be used.
My guess , is that this power consumption would be low, and not cause a drain on battery, since

• NFC is low power meant to exchange information within 5 cms




• NFC is active only when screen is on



• Since the tag information may remain unchanged, it may not require frequent polling


• NFC isn't quoted as a battery hogger in the battery drain culprits list (subjective)

Specific to your question, it would depend on

• How well the app optimises power ( it is not compatible with my device to see behaviour)


• NFC chip level power consumption used in your device


• How doze optimises (if using Marshmallow)

I would think that power consumption would be negligible, but it is a good idea to verify using an app like GSam Battery Monitor to see the actual power consumption and you could post your findings as an answer

Edit: Answer to Does NFC drain power if tag is attached constantly? on Electronics SE gives good technical reasons for why the consumption should be low