I’ve got an imax b6 battery charger (probably a clone). Here is an random ebay listing:
https://www.ebay.co.uk/itm/IMAX-B6AC-LCD-Digital-RC-Lipo-NiMh-NiCd-Batteries-Balance-Charger-Dual-Power-80W/363213322793
There are a few variant - inbuild power supply, external power supply, no powersupply - I went for the latter as I have a bench PSU that I use to power it.
The above charger can be used with a lot of battery types. I’ve got a couple of 24V batteries that are similar to these:
https://hobbyking.com/en_us/rhino-1300mah-6s-50c-lipo-battery-pack-w-xt60.html
24V might be overkill. I often find 12V easier/safer - depends on what you motors need really. The battery linked has low capacity (1300mAh) but I reckon it’ll keep you project running for 30mins. Don’t let voltage drop too much or you’ll damage battery.
Can you use PD power bank? Perhaps. As you said - you’ll need one of those switchers in order to trick it into delivering higher voltages. The yellow batteries linked above will deliver 30A whereas I imagine PD power bank might deliver 5A which I suspect is plenty.
The jetson nano requires a hefty step down converter - I think it needs 5v @ 3A.
Here is a random link to something that might do the trick but a named (decent) brand like pololu might be 3x price:
https://www.amazon.co.uk/ARCELI-LDTR-WG0200-Converter-Electronics-Accessories/dp/B07RGB2HB6/ref=sr_1_6