I purchased a 2019 Forest River FR3 30DS last year. Last time we took her out was around 2 months ago. I opened the door and the steps would not come down. I went to turn on the battery disconnect and nothing. I started up the coach and after it ran for around 5 to 10 seconds, I heard a click and then tried the battery disconnect and it came on. The battery indicator says the coaches batteries are full. Is this normal?
Your coach battery was dead. If you looked at the battery indicator with the engine running it just verified charging from the engine alternator. The battery disconnect is powered by the coach battery. The clunk you heard was the interconnect relay energizing to allow charging from the alternator. The steps extended from the output of the alternator added to the coach batteries.
I thought that they might be dead as well but here is the funny thing, after I started it, and I was able to switch over to battery, I shut the engine off and went back and checked the coach batteries. They indicated that they were full like I left them two months earlier and this is a brand new coach so the batteries don't have any age on them yet.
Well, the steps are fused directly off the coach battery so battery disconnect does not have any affect on them. If it happens again you might the entrance (screen) door open and go to front of coach and actuate the emergency start switch and see if the steps extend. If they do it is a coach battery issue. Of course strange things do happen when it comes to electrical issues.
Added: don't start the engine when actuating the emergency start switch.
Bubbles is correct. I would add that the disconnect does not disconnect everything from the coach batteries. There will still be a draw on the batteries that will drain them dead in that 2 month period. Add a disconnect between the negative terminal and ground or use a battery tender.