Battery connect or disconnect?

Recently a fellow RV'er was helping me replace the seals in my wheel bearing area and take care of that business. As we discussed other 'to-dos' around the Airstream, he said to leave the battery connected or hooked up while I was hooked up to power. I am not sure of this as the former owner told me to dis-connect it. The P.O said if left hooked up - the battery would continue to charge and could damage it. It's a large battery at that. So to be on the safe side I am going to disconnect it today. What are your opinions? I will be watching my emails for you response. Thanks, Bill