Hi there!
I had a battery drain in older versions. I tried to wipe all data, partitions.... and still with battery drain issues. The only solution was flash Clean ROM from fastboot and MiFlash. I don't know why, but I hope this helps you.
Hi friend, I recommend reflashing ROM with MiFlash tool (using .tgz ROM...) probably something is wrong in ROM. After that check it. If you continue with problems probably something is wrong in phone.
I've tried to downgrade, and install new global rom and it worked.
Probably you Wipe system and may cause a problem. Use only factory reset to update it worked for me.
As "ximio" said, if you have unlocked BL you can download Xiaomi FlashTool and install Rom frome there.