they are 12 volts
It is 12 volts.
It is 12 volt.
Yes.
12 volt.
All Harley Davidson motorcycles have used a 12 volt battery since 1965. Prior to 1965 they used a 6 volt battery.
12 volt system A fully charged 12 volt battery will have 12 to 12.7 volts. With you engine running you should have 13 to 13.5 volts
how Can you charge multiple 12 volt batteries with a car?
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.
Depends on the battery size. If your boat is a 12 volt system and you wire two 12 volt batteries in series you then have 24 volts. If the batteries are 6 volt batteries you will be fine. If you have a 12 volt system on your boat and want to use two batteries then wire two 12 volt batteries in parallel. You will still have 12 volts but will have double the amperage available and this will extend the running time of the batteries.
you only need two 12 volt batteries to make 24 volt. connect them in series
No!
12 volt