This is a tougher question than might be immediately apparent.
The very easy answer is that a fully charged Lead Acid Battery should read between 12.6v and 12.7v.
Two things will make the battery meter on your RV show you a voltage that's not really the voltage of your batteries.
For a realistic reading on your RV's battery meter you need two things to be true. First, that no charge has been applied to your batteries in the past 30 to 60 mins. Second, you have to be sure that nothing in your RV is using any power from your batteries.
The real world facts are that there is almost no time when you are on your RV and neither of these things are happening.
If you are plugged into shore power, running a generator or even have solar panels on your RV those things are probably charging your batteries.
And, even though you may have all of your 12v lights and appliances turned off it's still possible that other "hidden" devices are using your 12v power.
So, you can turn off your battery disconnect, unplug any charging source and WAIT about an hour and then test your battery voltage level THEN and only THEN will your battery voltage meter display your actual battery charge.
2017 Winnebago Adventurer 37F
2016 Lincoln MKX Toad