I don't have Pi 4, but an Android TV box running kstars/ekos which needs 5V 3A as well. I use a 12V to 5V/3A Buck converter to connect to my Harbor Freight 3-in-1 Power Pack battery's lighter port. www.ebay.com/itm/Buck-Converter-12V-24V-...Adapter/191949377436 Adapters would be needed to connect to the USB C of the Pi 4.Read More...