Hi,
@nano303 - The OP currently has a 1+ year-old work iPhone and currently owns a Samsung Galaxy Tab S.
My iPhone 6S loses about 3% a day when unused (I'm still on OSX 9.x due to work requirements. I heard that OSX 10 has new battery issues). I don't really care how much battery my iPhone uses, since I don't use it much (not sure why people think Apple phones are so great - they certainly aren't easier to use, and almost always require more button presses than Android to do the same thing). Work will replace it eventually, so not a big deal. However, I did do some setting adjustments to the un-jailbreakable iPhone to get better battery life so it would comfortably make it through the day.
My 2+ year old Samsung Galaxy Tab S is running Schischu's excellent Marshmallow ROM, and currently loses < 2% a day when unused.
I did have a Galaxy S3 a while back, and it took a few ROMs before better battery life came along. Fortunately, the Galaxy S3 had an easily replaceable battery, so battery drain wasn't as much of a concern.
What I have discovered is that when mobile phones aren't designed with user battery replacement, very few - or, no - options exist for purchasing a quality replacement battery. There aren't any quality OnePlus One replacement BLP571 batteries available in the US (though, there is apparently one manufacturer in Germany who doesn't ship to the US). So, fully-functional mobile phones get thrown away for the most unnecessary reason of all: the battery died. The OP3T has really good hardware (if this battery thing gets figured out). If I could keep ours running and just replace the battery every 3-4 years, that would be great - I don't think there are any real hardware upgrades in the future that would incentivize me to replace.
Yep - The OP3T is a $440 phone. So, as I mentioned above, I buy two phones when family replacements occur: One(Plus) for me, and One(Plus) for my wife. So, that's $880 when we replace. I expect that OnePlus will continue slowly increasing their phone prices as they gain more recognition, so that dollar amount is likely to increase next time.
Now, with regards to getting better standby battery on the OP3T, I have made some progress ... I reinstalled FreedomOS 1.3 for the OP3T, and trimmed things back quite a bit with the Aroma installer to see what is possible for a baseline. I'm seeing about 0.2%/hour battery drain when in standby. I will provide more details and updates later today.