How do you make a 6 volt battery into a 12 volts?
That is Impossible. You can however make two 6 volt batteries
into a 12 volt system by wiring the two 6 volts batteries in
Series. You will then have an output voltage of 12 volts but the
amperes will only be what one of the batteries have, In other words
the volts will double but the amps will stay the same as if you
only had 1 battery connected.