I recently purchased a 2006 Heartland Bighorn 3500 RL. Everything works fine while the battery is charged. With the RV plugged in to 50 amp service, the battery drains then I have no power to run the ac or anything else but the ceiling fan. I did not receive an owners manual with the rv. Is there a switch somewhere I am missing? With the rv plugged in to the 50 amp service, shouldn't I have power all the time? Any help would be appreciated.