Electrical Help Please

[426WARRIORMAN]

Have a Vento Zip r3i scooter and put a new battery in it and have rode it several times in a few days. I parked it for about 3 days and went to start it and there was no juice. I put the battery charger on start and started it right up. So I put the battery on charge and tried it again and it spun right over. Now that I think about it this problem existed last year to and my son bought a battery then for it, I know the scooter is charging when its running too. What I need to know is.............How do you check to see if there is a current draw on the battery when key is off?
I need to know this so I can try to track down what is running these batteries down.
Please let me know
thanks