With the battery switch on, when you press the test button on the monitor panel in Roadtrek the battery column of LEDs light up to show you how much charge is in the coach batteries, The top C green LED indicates that the Roadtrek is charging (if plugged in, running the generator, or running the engine). The next LED down - G amber LED - if lit indicates that the voltage is approximately between 12.5 and 12.7 volts (12.7 is considered full charge). The next two LEDs down to the bottom of the column - both RED LEDs - indicate from the one below the G to the one on the bottom that the batteries are 12.4 volts for the upper one and 12.3 volts for the bottom one. When the upper red LED is lit at 12.4 volts the batteries are at half charge - and at this point the Roadtrek needs to have the batteries charged by either plugging in for 12 to 24 hours, running the generator (which is the slowest way to charge), or taking a two to three hour continual drive on a limited access road at the speed limit. BUT with the monitor panel battery column what you are seeing is not exact but an approximation of the level of charge. If you want to see an exact battery voltage level you need a multi-meter - an electronic device that will read both AC and DC voltage (separately) by putting a positive and negative probe on the battery terminals. You want a multi-meter with a DIGITAL display. Using one with a dial and needle is not going to be easy to read. These can be found in Home Depot or Lowes or any electronics store or auto store - or on line. A digital meter will cost about $40 or more but is well worth it both for the Roadtrek and at home. Prior to 2011, Roadtrek had the battery(ies) in a slide out tray inside an outside cabinet on the passenger side of the van. This was either one or two cabinets - when there were two cabinets there was a battery in each. When there is one cabinet both batteries are in that cabinet. When these cabinets has sliding trays it was easy to slide the tray out and have access to the battery terminals. In 2011 Roadtrek changed from using deep cycle RV wet cell battery(ies) to no maintenance AGM batteries. With no way to open an AGM battery and no need any longer to check battery fluid levels - there was no need to access the top of the battery(ies) and since Roadtrek did not want you to even attempt to do that - they took away the slide. Here is a photo of my 2011 190 Popular with AGM batteries with the battery cabinet door open -

With this getting to the terminals of these two 6 volt AGM batteries wired in series to output 12 volts DC to the Roadtrek is a major pain as the batteries need to be lifted out as it is awkward to get to the terminals needed to take a reading with a meter.
BUT - there is a simpler way! For Roadtreks equipped with a TrippLite Inverter/Converter/Charger you can easily get a reading right from the battery connections going into the TrippLite. This works with both the earlier TrippLite 600 and the TrippLite 750 that Roadtrek uses later.
This is the TrippLite 750. This is located in the back of the Roadtrek behind the passenger side cargo door. To see where this is and how to access it - in many Chevy based Roadtreks - but Roadtrek over the years had a way of putting things in different locations so it is possible yours may be elsewhere -
this linked article will help you get to it (with photos) in the same location mine is. One thing for certain it is inside near where the battery(ies) are outside.
Take a look at this photo on the bottom left. There is a black cable and a red cable - the black cable is the negative battery cable coming DIRECTLY from the battery(ies). The red cable is the positive battery cable coming DIRECTLY from the battery(ies). The TrippLite is directly connected to the battery(ies). IT BYPASSES THE BATTERY DISCONNECT/CONNECT SWITCH ON THE WALL INSIDE THE ROADTREK. THESE TWO CABLES HERE ARE ALWAYS LIVE - THEY HAVE POWER GOING THROUGH THEM EVEN WHEN YOUR BATTERY SWITCH IS OFF AND/OR THE ROADTREK IS COMPLETELY SHUT DOWN.
NEXT - take a look at the top of the BLACK cable in the photo - SEE THE SCREW HEAD THERE. That holds the cable into the TrippLite. There is the another of that SCREW HEAD on the top of the red cable (hidden in the photo by the red cable - but it is there just as easy to reach. (Don't touch the two at the same time with your fingers - these are live connections.)
NOW - Take out your multi-meter - set it on DC - if there is a voltage range set the range to include 12 volts. There will be a probe with a red wire and a probe with a black wire that you plug each into the meter. Some meters have a button to hold the reading on the screen once the reading is taken and this makes it easy to look at once you have crawled out from where the TrippLite is located, stand up outside and read what it says - especially if you have a Roadtrek with a power sofa bed and the TrippLite is under the bed and the bed frame is in the way of the TrippLite. Once your meter is all set - and you can get it set up even before you start - you can take your reading.
HOLD each probe, each in a different hand and put the metal tip of the probe on the top of the corresponding battery cable screw head. Hold the probes away from the metal tip on the end of each prob. Do this not plugged in, best if the battery wall switch is of inside so there is no draw on the batteries when taking the reading, van engine off, generator off. Inverter wall switch OFF . Instantly the meter will display the exact voltage of both batteries - or your single coach battery on its display screen.
That is all there is to it. No struggling with battery(ies) in a small cabinet - no need to slide out anything. You just use this easy access method to see what the exact voltage of your Roadtrek coach battery(ies) is.
This is the meter I have. I bought it either in Home Depot or Lowes. This meter comes with the standard probes but it also has a temperature probe used to show the temperature coming out of a air conditioner, etc. It uses batteries to run but I do not keep those batteries in the meter unless I am using it - as I am not using it often. The pouch came from Walmart - though I have not seen these there in awhile. In the pouch it is an easy grab and go with everything needed inside to use it. I keep it in the house and it is on the what to pack into the Roadtrek before a trip check list. It is easy to find a place for it inside the Roadtrek!