If you are referring to the main battery cable use 00 guage cable.
can 6 ,12 volt battery be wire to make in to one 24 volt battery for solar use in home
Use 8 gauge wire.
4 gauge wire.
Place a current meter (rated for several hundred amps) in series with the battery. Or Place a large gauge wire of known resistance in series with your battery, use a high precision volt meter to measure the voltage drop across this piece of wire, then divide the measured voltage drop by the resistance of the wire. This will give you the current traveling through it.
The recommended gauge of wire to use for a 12 or 14 gauge wire is typically 10 gauge wire.
It depends on the voltage, but if you are using it on a 240 v system, it's quite OK to use wire that can take 600 v (if you had to buy the wire, you would be spending too much).
No
No, it will overcharge the 6 volt battery.
No it will not work
No, the battery will be overcharged and battery damage will occur if it is done.
No.