I was assuming that since OP said "battery draining QUICKLY", that there would be enough amperage pull to light a 12v bulb, but as pizza said, I could be full of it ... ( I usually am )

a milliamp meter, or amp meter would be the correct thing to use, but not everyone has easy access to them ......

I had recommended to someone else in another post to go get a cheap cigarette lighter voltage meter for the alternator test, I will again suggest that here.