There are 6 volt car batteries, but you are only likely to encounter them in really old cars, like late 50s early 60s.
Modern automobile batteries are 12 volts.
The charger needs to be set to charge for the voltage that the battery is designed to produce. Most car batteries are 12 volt batteries.
Automobile batteries today are all 12 volt. Most auto manufacutures switched from 6 volts to 12 volts in the 50s.
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.
DC definitely, all car batteries - all batteries.
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