if the charger powers on when you plug in the battery you should see it change status. Are you reading the output voltage while the battery is connected?
the reason i ask is if the charger is working you will read more than 48v, if 48 is what your getting on the vom then your just getting the voltage from the battery itself through the connection. If it is charging you should see that reading increase far above 48v.
have an electrician double check the connections, make sure the charger is setup correctly for 208v and all the line fuses are ok.
from the sounds of it you have it connected to power but the start relay is not kicking in when it senses the battery plugged in.?
i did a search for that charger but there isn't much info coming up on it other than one or two hits on ebay. I saw no hits on Hertner itself, they may not even be in business anymore.