I just feel like if im willing to deal with the added size of the extended, which i am, why carry 2?
There must be an extended that actually works as advertised.
I don't care if you carry a 10 billion Amp extended battery in a 55 foot trailer behind you. When you absolutely positively MUST make that one last call and the extended battery dies, you're up the proverbial body of flowing water without the proverbial eating utensil.
When my battery dies I can swap in the spare and know, without any doubt, that I have at least a couple of hours of use left.
Besides, the larger the battery, the longer it takes to charge. I don't want my phone tied up for 72 hours every week charging the battery. My "in-use" battery charges in a couple of hours in the phone, while the spare (assuming I killed them both that day) charges in the external charger in the same couple of hours.
And when it comes time to replace the battery (if you know of a company that makes a LiIon battery that will ACTUALLY [as opposed to "in the commercial"] last 35 years, let me know - I'll buy all of its available stock), I spend a few bucks for 2 new regular batteries. You spend enough to buy a small cellphone. (Given the same treatment, both the normal battery and the "extended" one with 10 times the capacity will last just about as long. Larger capacity doesn't equal longer life. Treating the battery does - while my Note 3 was in for "repair" [they ended up giving me a new one], I was using my Motorola V551. I was using the original batteries it came with - back around 2003. And getting just as much use as I got back then.)
So for a few reasons, I'd rather carry 2 batteries made by a company that makes good batteries, rather than one gigantic one, even if made by the same company. I've been the "battery on the belt" communications route (I've been in this business since "portable" meant "only takes 2 strong men to lift", and I'd rather not re-invent 1970. I want communications when I need it (one of my lock screen icons is labeled 911) and I don't want to have to nail my pants on to keep them from falling down.
Just one old man's opinion. Your mileage probably DOES vary.