You can generally pry the tops off of a "maintenance free" battery and check liquid level I do this to my camper's battery annually, the coach batteries have caps.
And to the OP, I completely discharged the group 31 battery in my Lance a few years ago. Was in a hurry and switched the refrigerator to 12v instead of off when I parked it then went wheeling for 7 hours, talk about dead!!
It came back just fine and doesn't even seem to be weaker than normal.
Best of luck
The above post is just my experience/opinion which is worth exactly what you paid for it.
'05 Lance 845/'06 F-250 or '99 Alpine 36SDS Usually towing an '01 Wrangler locked on 35"s or moderate '98 Cherokee on 33"s (rear locker only)