Gary, as with all things, the devil is in the detail.
Many of the lithium based power banks quote power at native voltage for lithium cells around 3.7V, whereas for astro we usually need 12V or so.
AGM type batteries are a lot more cost effective, but heavier. For example, Jaycar’s 26Ah 12V AGM battery is over 8kg, whereas their 25Ah 12.8V Lithium battery is 3kg. The AGM battery is $129, the lithium $299…
There are other factors to consider though…lithium batteries can typically be discharged further without permanent damage, so more of that total capacity is usable.
The crux of it is how much power you actually need to carry. The AZ-GTi wont consume much while tracking, so your main power draw will be your camera cooler. During summer months, that may be as much as 2-3A per hour. You could compromise on this since most modern sensors (including the 533) really don’t need to be cooled like mad like previous generations. Cooling to 5C is sufficient in most cases.
I’d suggest setting up your rig and measuring the current consumed. Then just multiply by the number of hours you wish to image for, and add a little extra for good measure