Charging a battery bank with Solar Cells

So essentially bought one of these "solar battery banks" for a weather station project i am working on.
Long story short the power output for the built in cell is awful.
Now the question is, can I just hook up a bigger solar cell to a USB output and plug into the battery bank directly to charge it? For example;

Solar cell – usb – battery bank
rather than
solar cell – charge controller – usb – battery bank

I know that these banks have their own internal charge controller so assuming I get a 5V output panel would this be ok?