Here is a stupid question that has always troubled me.
I am most familiar with control transformers; i.e., 480 vac to 120 vac. However, I know that Xfmrs work "both ways" . If i input 120 vac into that Xfmr i will have 480 (nominal) vac output.
For that reason i always disconnect bat chargers because i am afraid the charger will drain the battery when I unplug the charger.