I went from a Moto G 2015 to a Moto X Pure (North American version of Style) and that is my only real complaint... the battery life easily cut in half or more. Although some of the reasons for it are listed in previous posts, one is missing, the SD808 SOC's radio is a battery hog especially when signal is not optimal, a mediocre connection will kill your battery especially if you actually make or receive calls, but if you have great signal then it sips battery very efficiently.
The main battery drainers are the 5.7 QHD Super LCD display (this display panel is incredibly inefficient, but beautiful), the SD808's radio, the SD808's architecture (2+4 big.LITTLE setup in this chipset is much less efficient than anticipated, probably why the configuration was dropped), and the poor battery size choice (it should have been 20-33% larger) makes this device seem like a terrible "upgrade" to the Moto G, battery-wise at least, and in that regard it is correct.
But the very things that draw battery are it's strengths... the display is gorgeous, it can be seen clearly in full daylight and is incredibly vibrant and sharp, and side-by-side to the Moto G 2015 it makes it's little brother's display look like an old 20" tube TV vs a 55" 4k UltraHD display. The SOC may not be very battery friendly, but it is much more powerful and it's reception is excellent, even with poor signal it will hold service well, at the cost of battery life (note that Moto did NOT implement Jio VoLTE in this device, and will not, a significant letdown since it is working on similar Moto devices of that generation), and the QuickCharge 2.0 will refill the battery very quickly, around 75-90% in an hour if necessary.
It's kind of like comparing a Chevy Cruze to a Corvette, one is simple, reliable, and very fuel friendly, the other is a performance machine which sucks gas like nobodies business... but they are for different purposes entirely.
As far as custom ROMs go, I have not found one that gives better than near equal to stock... After trying a dozen or so ROMs and kernels, I went back to pure, unrooted, stock and haven't looked back in a few months. It isn't ideal, but until I can get a better all around device it will have to do.
