Solar car battery charger

I have a project I've been wanting to create for years which is a solar spa
where the entire setup runs off the grid completely. No 120VAC is desired.
I already have an RV pump which pumps water from the spa back to the spa
(after running it through a long black hose of probably hundreds of feet).
<https://www.amazon.com/dp/B0DF7B1VYD>
I tested that pump today on an old battery and it seems to be working.
a. It pulls water out of the spa via a garden hose on the pump input.
b. And it puts it back via a garden hose on the pump output into the spa.
The specs on that RV pump are 12VDC, 4.65Amps, 8.0 Amps maximum.
I have three spare car batteries (which probably aren't in the greatest of
shape as they're old batteries which friends discarded & gave to me).
All I need now is the solar panel setup. But I know nothing about solar.
I'm sure I need a panel and some way to control the battery charging.
What kind of panel do you think I need?
And does it need some kind of control module to charge a car battery?