I would have to agree with 2 of the above posts. 1st any meter will read the correct voltage. I feel from working on RV's for as long as I have & also have been on a tech support desk for Monaco for several years before starting my own business that 2 things every RV owner should have on board is a voltage meter & battery charger. That aside the 2nd thing is that the controller board is more than likely defective. Most of the time these can be replaced by a inverter repair facility. There is a good one in Phoenix AZ. With all inverters the 1st thing & easiest is to power them down for a reset. Unplug coach, disconnect battery power at the inverter & wait 5 minutes. That does a reset of the unit. But your unit is for sure a bad controller board. As stated in the post above you could try to repair it yourself. But a word of caution should go with that. The repair shops can test the unit to make sure it is operating correctly ( load outputs, charge outputs, Ect.) Unless you are sure you know what you are doing I would send it in. Check the companies website to see if there is one close to your location. More than likely there is one close. You can take it to them & have it back in a few days. Or you could see us in Yuma in the fall.
Hope that helps.
Rob Pierce
Sunbum RV LLC