My 5er has 2 12v batts. We just spent 2 nights boondocking. Ran the fan on low for at least 30 hrs. We also used the radio for a couple of hrs. 1 LED and 1 florescent light were main lighting for meal prep and eating both nights. Water pump for showers and dishes and regular RV lights in bath and bedroom. After 48 hrs my DC volt meter showed 12.34 at rest, starting voltage was 12.67. I have volt meters mounted just inside the door and always check them entering.
Forgot I also ran a 02 fan on 12v in the bedroom for at least 6 hrs each night.