I'll be in deep woods for about 2 weeks, no way to re-charge anything unless I bring a power bank or two.

I need you engineer types to help a simple HS teacher out.
Do any of you have experience with one you like that you'd recommend?

Is there a brand I should stay away from?
A brand I should run to?
Should I trust what they say are the charge capabilities (i.e., is there a standard that's enforced?)?

Is 20000mAh really 20000mAh?
I saw a pop up ad (it's on the internet, so you know it's true!) for a 40000mAh @$50

I'm looking to go relatively inexpensive, but I'm thinking at least 6 phone re-charges (I'll only be using phone for photos, short vids). If I get a great one, maybe I can even listen to some tunes at night around the fire. My phone with light use can go 3 days. (I'm not in sales or 'consulting' anymore).

I do already have a Mac; it came in a box which I promptly cut a hole in, and showed to my hookers when I brought them some blow. Not sure that'll help me in the middle of nowhere.

Oh great minds of the lounge, what say ye?

TIA!