Can you charge a 6 volt battery from a 12 volt source?

Answer 1

The simple answer is NO. Why not use a simple 6 volt power suppy from some junked piece of audio or telephone equipment, Just watch the polatiy when you make your connections.

Using 12V on a 6V battery can fry your battery but not the otherway around.

Answer 2

No you cannot charge a single 6 volt battery on a 12 volt charger. You can charge two 6V batteries on a series circuit, positive pole of one battery connected to the negative pole of the other, and the remainder poles connected to the 12 V charger.

Another possible solution to this problem is to connect a wire resistor on a series circuit to the 12 charger in order to lower the original voltage to approximately 6 V. But this requires a good knowledgment of electricity specially to calculate the correct value of the wire resistor. The calculation of the ohmic value for the wire resistor must be based on the Ohm's Law. It is possible that a bulb serves as the wire resistor to make the voltage to drop to 6V. This way you can charge a single 6V battery without having to use a couple of 6V batteries.
That's probably not a safe thing to do. HOWEVER: What you CAN do safely is to charge two 6-volt batteries in series at once. Connect the positive terminal from one battery to the negative terminal of the second battery. Now connect the proper leads from the charger to the remaining battery terminals and voila!
No. Severe damage can result unless you are a car electrics specialist and know what else to use as well as the two batteries, to limit the flow of current to a safe amount..