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Check the advanced settings, by default the keep wifi on during sleep is set to always, this will drain the battery by maintaining the connection even when not in use
I use 'Easy Battery Saver', which is also free, and has several power-saving modes, including a completely configurable 'Advanced' mode that allows you to specify what happens when the phone locks & sleeps, variable display brightness, what to do when the battery gets low, how to manage wifi, mobile data, bluetooth, syncing, and sleep and night scheduling. Or you can pick pre-set 'General', Intelligent' or 'Super' power saving options. There's also an option to turn off all and allow the phone to behave as normal. Only drawback is that it shows small ads, although they're not intrusive.
It works well for me.