I found a new one on Ebay.
No you should not do that. It will damage the battery and the battery will explode.
The battery is a 12V car battery.
The largest battery in size is a 6V or 6 Volt.
No, it is a disposable battery.
If it is in your car then no, why do you have a 6v battery in your car in the first place it should be a 12v.
You don't.
Usually 6v, can be 12v.
It'll say 6v or 12v written right on the battery.
Connect 4 in series.
12v
A 6v motor might not run at all on a 4.5v battery. Whether or not it does, it's likely to discharge the battery rather rapidly. A series resistor will help the battery last longer, but will make it even less likely that the motor will run at all. You're better off taking some time to find either a 4.5v motor or a 6v battery.
Adding a seound battery to a series circuit will increase the voltage, and require less current to keep the lights (if there are any on) as bright. Say you have a 6v battery, then you add another 6v battery. the voltage of the circuit would be 12v