batteries - Using a 12V battery while simultaneously charging via solar panel

I have a couple of 12v batteries that I'd like to use to power a cooling apparatus while camping for several days.

I also have a 15W solar panel I'd like to use to top-off the battery.

Can I use the battery while it is charging? Or would I have to disconnect the solar panel prior to using the battery?

Alternatively, I could charge 1 battery while using the other, and simply swap them out - is this preferable?