Cables

There's a few factors involved here.

Does your panel(s) have MMPT controller built in or are feeding say a Ctek charger?

What power rating is the panel?

How big are the existing cables?

With those answers in mind- vacuum cleaner cables is very low current cable and only has to pass an amp or so. Its the amps capability that is key here. If you have a long cable and try to pull lots of amps through it, you will lose volts along the cable. If you were trying to pull say 6 amps out the battery end you might only have say 9 volts hence no charge capability.
You need to make it at least the same size as what came with the panels but that's a minimum. The longer the extension cables then the more voltage drop will occur requiring bigger and bigger cable.

If you are using regulators at the panel end then they are reducing the voltage fed into the cabling which means any volts drop is very critical. If no regulator and just the panel fed to say a Ctek then the voltage in the cable will be much higher allowing you a bit more leeway with volts drop.

Going to be a bit of trial and error on your part juggling cable length and size against finding somewhere to store it.

As an example, I think my panels are around 120w, regulators are bypassed and I use a Ctek. The panels factory cable is about 5 meters long and something around 8B&S in size which is adequate for that power and length but only just.
Have a 15 meter extension for this which is 6B&S (thicker). Again this is really on the light side and should be bigger but it does the job for me and keeps up with our discharge rate so I can't bothered doing more. 20 meters of thicker cable takes up a lot of room plus its heavy.

So, back to your question, if you have nothing else then try the vacuum cleaner cable but its not likely to do much for you.

Thicker and shorter the better when talking 12v or 24v. Usually upper limit is what you can squeeze into connectors or can afford. This usually end up as #6 B&S (awg) as it fits into anderson connector well. If you choose cable based on current rating it will be crippling on volt drop. You can more or less ignore voltage rating as it is unlikely you will run into a cable with less than 25v insulation