solar panel setup

1) Figure out the current you are expecting
2) Find the wire gauge for the current you are expecting using a website like this one.

What are you using it for?
16 gauge will likely be sufficient, 14 gauge to be absolutely safe.

You know lead acid battery is not ideal for charge/discharge situations rite? (Although the alternatives are so absurdly expensive, for that reason it is still probably the best option)

Current between the solar panel and the controller will be highly variable, so dont skimp on that.... between the controller and the battery should be a lower and more consistent current. Then between the battery and the item you want to power, depends entirely on what that item you want to power is?

Are you using deep cycle batteries like a marine battery? Car batteries won't work well as they are starter battery. All juice up front.

Also if he connected multiple batteries in series, that will divide the recharge and discharge current between them and greatly reduce the wear and tear on the individual battery.

Edit: not in series... parallel!

Wiring them in series would multiply the voltage and would be kinda explosive!

The lead acid battery is not safe to recharge, people use Li-Ion battery house like Anker and Ellon Musk's power system, they are more safe and durable.

How very odd. I've been using lead/acid batteries in my cars for over fifty years without a problem. They recharge every time I turn on the engine.

What on earth are you thinking of?

Perhaps it’s because you don’t charge it with spam that keeps you safe?

Maybe. I charged them, not fed them.

If you have only one panel you probably are talking about 100 watts, and that is not a heavy current. Nevertheless, you should hire an electrician to hook it up. He will charge you a few bux, but it will be cheaper than a fire and it will be done right the first time.