Can I connect a 5w 5w solar panel directly into a 10k mAh portable battery bank safely via USB 2.0, or does it need some sort of protection in-between like a solar charge controller or a schottky diode?
Example of battery bank (except one with usb 2.0 input): https://www.anker.com/ca/products/a1229
Example of solar panel: https://www.aliexpress.com/item/1005006012344670.html
This is very helpful. I actually have two of those panels so I can try wiring them up in parallel.
I also have that exact USB monitor which is super handy.
Excellent. What does the monitor show for volts with full sun and no load?
To parallel them, you might get away with using an (very) old USB v1 hub. Or solder something up from the junk drawer or parts from an old junk pc