Motorcycle batteries may be 6 volt rather than 12 (check this) and if they are 6 volts, switch your battery charger to 6 volts or you may damage the battery.
No, not if the motorcycle is wired for a 6 volt system. This must be a very old motorcycle.
No!
Yes, if the two 6 volt batteries were connected together in series.
The majority are all 12 volt.
Two 6 volt batteries in series, yes. In parallel, no.
You cannot use a 12 volt charger to charge 2.6 volt batteries. The 2.6 volt batteries will become hot, very quickly, and explode.
Two six volt batteries in series makes 12 volts so switch the charger to the 12 volt position.
Modern automobile batteries are 12 volts.
Depends on the amperage of the batteries you are using. Both setups will give you 36 volts, but you will normally have a longer run time with six 6 volt batteries in series than three 12 volt batteries. That is why golf carts use 6 volt instead of 12 volt batteries.
they are 12 volts
Paralleling four sets of 6 volt batteries will still give you 6 volts. Two 6 volt batteries in series will give you 12 volts. Parallel these series sets will give you longer endurance at 12 volts. There is no way you will ever get 48 volts out of four 6 volt batteries.