In fact, we have another source of battery draining: `Allow always scanning' in `Wi-fi advanced' setting. Unfortunately, LeEco hides this option in that page.
If we have root access, we can use SQLite Editor to switch this off by editing the settings.db of Settings Storage. The database is `global' and the table is `wifi_always_scanned_enabled', change the value to 1 and reboot would do the trick.
I have pictures of these stuffs but I can't post images in this forum as of now.