I turn on data saver and allow few apps like social media that really need a background usage and this helped me to save a lot of battery, i can lose only 3-4% overnight with this. try it and tell me if it works
Battery life on any phone is completely subjective and very much depends on the number of apps installed, the type of app and how you use your phone.
Anyone who says "this ROM's battery is great" or "that's ROM's battery is amazing", is only speaking in terms of how they use their phone and what settings are enabled.
The golden rule of battery life is quite simple, the less your phone has to do, the less battery is used its as simple as that.
For example you can have 2 devices running Nougat both with identical apps installed. One phone is used normally throughout the day with auto update apps, screen brightness on 50%, volume on low, Bluetooth on blah blah and its lasts 12 hrs.
The other device is just used for texts and calls, has auto update apps off, screen brightness at 30%, volume at 30% Bluetooth off and it lasts 16 hours.
With all these different variables it is nonsense to suggest one rom is better than another, battery life involves so many variables you simply cannot work it out with any degree of accuracy. Anyone who claims otherwise is tripping.
The slimmest barebones ROM's are lineage and other ASOP ROM's. If you want your battery to last longer start with these ROM's.