I've used Geekworm stuff for a while and I've been impressed with the performance and support. I just noticed they have a UPS board that incorporates 18650 batteries. It does provide auxiliary 5v output and safe shutdown, but needs to be powered by 5v.
https://raspberrypiwiki.com/X750
As for a 12v/5v converter, here's the one I use. Plenty of headroom.
https://smile.amazon.com/gp/product/B01ENT1O62
https://raspberrypiwiki.com/X750
As for a 12v/5v converter, here's the one I use. Plenty of headroom.
https://smile.amazon.com/gp/product/B01ENT1O62