These two power banks are all you'll need, and you can spend less than $80 for BOTH

Two of Anker's power banks are on sale for Black Friday/Cyber Monday, and you can spend less than $40 on each.

source https://www.androidcentral.com/accessories/power-charging/these-two-power-banks-are-all-youll-need-and-you-can-spend-less-than-usd80-for-both