[Nexus 5X General] jimv1983:
I understand what you are saying about wake locks and have experienced it first hand. Once my Nexus 5 was updated to Lollipop there was a wifi wake lock issue with my work's wifi(it wasn't present with Kit Kat) that would cause the phone to never sleep and would be dead in a few hours. Assuming a phone is behaving properly(deep sleeping when it should) then it will last a long time on even a small battery if not used that much.

The main purpose of a bigger battery would be to handle issues where the phone isn't sleeping as much as it should(obviously never sleeping would still be a problem), being in areas of lower signal and mainly heavy usage all while still being able to last an entire day. Actually using a phone is what kills the battery the fastest whether or not that is because of the CPU and other things happening when in use or mostly because of the screen(I know we disagree on this) having a bigger battery would help this a lot.

My Nexus 5X could go days in stand by but with actual usage it lasts 3-4 hours screen on time with about 14 hours off the charger(with one day getting 5.75 hr SOT over 20 hours which hasn't happened sense even with the same usage conditions.

Based on the screenshots from this thread and the thread about average screen on time(http://xdaforums.com/nexus-5x/general/sot-poll-t3233858) 3-4 hours seems about average. If the Nexus 5X had a 3,500mAh battery then that number could likely be up to 6-7 hours screen on time with the exact same usage that gets a Nexus 5X 3-4 hours with its 2,700mAh battery. That would also allow people that are now only getting 2.5 hours SOT to get closer to maybe 4 or 5 hours.

For me to consider a phone to have good battery life it would have to provide ~5 hours SOT over a period of 16 hours off the charger(an entire day minus 8 hours for sleeping) while taking everything I can throw at it. A moderate amount of gaming, mobile data the entire time, 30-50% brightness, moderate amounts of GPS, varying signal strength, browsing, social media apps, etc. Even if the Nexus 5X were to deep sleep exactly as it was expected when not in use(no rouge apps etc) there is no way it could get that kind of battery life with a 2,700mAh battery but it could with a 3,500mAh battery.

For me to consider a phone to have excellent battery life it would have to get through two days(to account for days that you might forget to plug it in at night before bed) of the same above usage(so 10 hours screen on time over 40 hours off charger).

For me web browsing seems to drain the battery pretty damn fast. In my experience on wifi with ~20% brightness in an area with good cell signal web browsing using Chrome drains the battery about 20% per hour.

There are people that are only getting 2.5-3 hours SOT from the Nexus 5X and regardless of the reason a bigger battery would absolutely help with that. If the Nexus 5X had a 3,500mAh battery then even a somewhat badly behaving phone(obviously not a phone that NEVER sleeps) would last a full day with 4-5 hours SOT.

As far as phones with bigger batteries getting the same battery life that is often because of a much higher resolution. Compare the battery life tests from Phone Arena for the Nexus 5X vs the Nexus 6P. Both phones were tested under the same conditions(probably with no other apps running) and despite the fact that the Nexus 6P has a ~28% bigger battery and a supposedly more efficient SoC it actually LOST to the Nexus 5X by one minute.