Fully charged should be around 12.8
No, you cannot charge an 8 volt battery with a 6 volt charger. The voltage of the charger must match the voltage of the battery.
Since this question is in the car battery category I am going to make a couple of assumptions:Most 1960 vintage and older automobiles were equipped with a six volt battery, the minimum usable voltage of these batteries is 6.1 volts fully charged is 6.6 voltsMost 1960 and later automobiles are fitted with a 12 volt battery, minimum usable voltage is about 12.1 volts, fully charged is around 13.2 volts
yes more voltage
12 volt
Usually 12 Volt
No, the battery charger has to match the voltage of the battery it is to charge.
12 volt of an ordinary inverter battery
This is not advised! The 9-volt charger might have a current limiter so that nothing burns up, but it any case if left on it will destroy the 6 volt battery by overcharging. A 6-volt charger is not expensive.
Some have a switch for 6 or 12V - if not you will "cook" a 6 volt battery using a 12 Volt charger
12 volt.
Yes, it has twice the voltage power.
Can You Charge...Yes. As a matter of fact, in order to charge a battery, the charging voltage HAS to be greater than the charged battery's voltage or no current will flow and charging cannot happen.Of course, the charging voltage cannot be excessive, or damage to the battery being charged will result.In your question, 4.6 volts is not excessive for a 4.2 volt battery.