Can you use a 6 volt battery charger to charge 12 battery?

No, you should not use a 6-volt battery charger to charge a 12-volt battery. A 6-volt charger does not have the voltage capability to properly and safely charge a 12-volt battery. Attempts to do so can result in damage to the battery, the charger, or both.

Batteries are designed to be charged at the voltage for which they were manufactured. A 12-volt battery requires a voltage of 13.8 to 14.4 volts to be properly charged. A 6-volt charger will not be able to provide this voltage, and may cause the battery to become undercharged or damaged. Additionally, a 6-volt charger may also cause the battery to overheat or become unstable, creating a safety hazard.