inverter and start batteries

I own a 2008 Fleetwood 40x Excursion since new and my 2000 magnum inverter seemed to be making a little more noise than usual, I set the controls to factory default for the inverter in case they had changed some how. This morning there was a strong smell of acid coming off the starting batteries and I noticed a mist escaping from 1 of them.(they are sealed batteries) Has anyone else out there had this sort of situation with batteries and associated equipment. I am looking for advise as to what may have caused this before I replace the starting batteries. Cheers Blake