Default Battery Problem

Hi to everyone! I think to have a problem to battery. I do 2/2.30 hours of screen on, with 11/12 total. But today I have noticed a strange drain battery . I reboot my device and it has lost 6% of battery. What is the problem? Is it naturally?
I hope in one your explanation. Thank you!

Sent from my Nexus 5 using xda app-developers app
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Current Devices:
Nexus 5, Black version with 32Gb --->My treasure!
ROM: Android L Developer Preview
Bootloader: Unlock
Kernel: Stock
Recovery: TWRP 2.7.0
Old Devices:
Samsung Galaxy S2, Black version 16Gb --->To my daddy!
ROM: NeatRom
Bootloader: Unlock
Kernel: Stock
Recovery: CWMR