Another question here: Is the 7500mah bulkier than teh 5200? Or are they the same?
Edit: Nevermind, found this 7500 mAh which has the exact same thickness with the stock version, and does not disable NFC. I will research further but for now, this seems to be the best choice.
Link to non-mobile version for those that care about such things.
Here's an extended battery. Kind of like a battery case. It's just a huge battery that replaces your built in battery. That way it just increases your battery capacity and forget about it.
Zerolemon 7500mAh White: https://www.amazon.com/dp/B00CXZI3DQ/ref=cm_sw_r_sms_c_api_RWbKxbTP9Y1RF
Zerolemon 7500mAh Black: https://www.amazon.com/dp/B00CXZI3DQ/ref=cm_sw_r_cp_api_RWbKxbTP9Y1RF
Anker 7800mAh: https://www.amazon.com/dp/B00GNQ10VS/ref=cm_sw_r_sms_c_api_mZbKxbK9DWQYK
Anker 5200mAh: https://www.amazon.com/dp/B00CPLMG86/ref=cm_sw_r_sms_c_api_9ZbKxbYSZFBFA
Personally I'd just go with the Anker batteries. They're just cheaper in this case. I've bought stuff from both brands and they're both pretty reliable.
I have this 7500 mah Zerolemon battery. Downsides are that the phone is now bulkier, there is no flip cover, and my wireless charging no longer works.
The upside is that although my battery is about a year old, I am getting 3-5 days' charge consistently. Proof.
Disclaimer: AOSP Marshmallow custom ROM and outside the normal text, calls, browsing internet on the toilet/at stoplights, I mainly use my phone to stream BT. Stock Lollipop ROM I was getting minimum 2 days with average use.