The Panel on the Charger (there will be a switch here too) will say > 6 volt, 12 volt, 12 volt < across the top! You are charging a car battery, so you do need 12 volts only! But you need to distinguish the amperage you want to use and that is read under the 2- 12 volt choices on the panel you are reading.
Two six-volt batteries can be wired to equal a 12-volt battery. Batteries wired in series can be charged to the capacity of the weakest battery. Batteries wired in parallel will equalize the charge, with higher charges flowing to lesser charges until equalized. SLAs generally take six to 18 hours to charge.
Frequent short trips, with constant stopping and starting, make your battery work. it delivers 1 amp for 48 hours, 2 amps for 24 hours, 8 amps for 6 hours and so on.. to change the mains 110/220 volt alternating current to 12 volt direct current .
Car cigarette lighter voltage and amps,12 volt car battery charging voltage, charger. A: A 12V car battery can be charged over a range of voltages.. . so a flooded lead acid battery will still have 50% of its capacity remaining after 6 months.