Wanted to post this in case others were looking for the same.
Been looking for something that can power the Pi4 all night but is portable/mobile. All the power banks I have are supposedly 2.4A @ 5V but the voltage dips a little when current is drawn, causing undervoltage errors on the Pi. I know the Pi 4 is rated at 3A but that's under full load.
Took a gamble on this guy and have been very pleased with the results:
"Charmast Power Bank with Led Display 23800mAh Quick Charge 3.0 PD18W USB C Battery Pack" www.amazon.co.uk/gp/product/B0892B32LB
It ran the Pi4 today for 2 hours and it dropped just 10% battery without a single undervoltage error
I connect the RPi with a ASI120MM-S and an ASI533MC attached and a OnStep mount driver (consumes below 2A) and I've been able to run the setup for more that 6h
About the ASI533MC: the cooling is connected to a second battery. If I try to connect the cooler to a single battery, I overload it and it stops. So the easy solution was to use a second battery (of the same kind) to run the cooler.