This is my favorite thing. I have it in my bag with a long USB cord looped in. This particular model can charge my Samsung Note 4 5 times or so per full charge of battery.
There are cheaper models as well by the same manufacturer. Anker is also popular.
I'm going to grab one more just to have.
I've been using this one from RavPower for the past five months. It went all over Thailand with me in March and April, it works great. https://www.amazon.com/Qualcomm-RAVPower-20100mAh-Portable-External/dp/B0156HCJQO/ref=sr_1_2?ie=UTF8&qid=1468712797&sr=8-2&keywords=ravpower+20100
I left verizon in november, couldnt be happier. service with verizon was a bit better, but wifi is fine where service is bad.
I had no problems
I also like to have a fuck ton of charging options everywhere I go, rather than keep one with me all the time. you could do the adapter route that you linked to, just know you will be limited to 1.5 amps no matter what amp charger you use, its by design of the 6p. for usb c cables, chargers and misc, look at this spreadsheet https://docs.google.com/spreadsheets/d/1wJwqv3rTNmORXz-XJsQaXK1dl8I91V4-eP_sfNVNzbA/edit#gid=0&vpid=A2
I hated the idea of charging so much slower, so I bought one of these
http://www.amazon.com/gp/product/B017BVLLC6?psc=1&redirect=true&ref_=oh_aui_detailpage_o00_s00
and one of these http://www.amazon.com/gp/product/B017I7EX46?psc=1&redirect=true&ref_=oh_aui_detailpage_o03_s00 for ac charging
one of these http://www.amazon.com/gp/product/B014F2NQ36?psc=1&redirect=true&ref_=oh_aui_detailpage_o08_s02 for car charging
and this for portable charging http://www.amazon.com/gp/product/B0156HCJQO?psc=1&redirect=true&ref_=oh_aui_detailpage_o06_s01
it gives me 3.5 charges
1500mAh is only a 1.5A charge. That's standard for most battery packs, nothing great. My old Motorola P4000 charges at 1.5A.
This Anker 20,100mAh on Amazon is $79.99 (not Prime) and supports up to 2.4A on standard USB and 3A on Type-C.
Here's a similar Anker 20,100mAh one without Type-C for only $45.99 (Prime). It is limited to 2.4A like all standard USB ports though. It does come with the wall adapter too however.
There's also this 20,100mAh one from RavPower for $55.99 (Prime) that's the same capacity and 2.4A USB and 3A Type-C capability (except it also supports QuickCharge2.0)
Or this RavPower 26,800mAh behemoth for only $49.99 (Prime) without Type-C that will charge up to 2.4A via stadard USB.
Both of the RavPower devices have good reviews and I've never had an issue with them or Anker before.
Aukey is a trustworthy brand, similar to Anker. I use their chargers and their 10000 mah aluminum QC2.0 battery (though obviously it doesn't do QC2.0 on the 6P). I'm waiting for a discount on this (below), since my philosophy is that if you're charging your phone with an external battery, chances are your battery is low. Which means you need a quick charge.
Damn, I literally just ordered the one that was "benson approved"
https://www.amazon.com/gp/product/B0156HCJQO/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1
What's the difference? They look the same, but they are not the same listing.