A few of them worked well, but continued to display the thunderbolt icon. I was trying to get a 10k mah rated battery as I feel that’s a good size/price ratio for a portable Pi setup.
This RAV Power performed the best. And lasts longer being 15k mah. https://www.amazon.com/dp/B082XC8BK7/ref=cm_sw_r_cp_api_fab_8DJCFbH5C6ZN2
I haven’t done legit runtime measurements but based on percentage of battery depleted after one hour I would say it will last at least 6hrs on one charge. And that’s being conservative with my estimate. Powering both the Pi and the 7” screen.
I see a lot of recommendations for Anker and I have to second that as well but if price is of any concern, RavPower has cheaper options for similar functionality. Keep checking out specific products on Amazon that perks your interest because more often than not it will go on sale or there will be a coupon. I have two of these and they fit my needs pretty well.