Inside your Roadtrek on the monitor panel, you can check the battery voltage with four LED lights. The lights will tell you C (top green light) for charging and indicates that the voltage is at or above 12.7 volts, G ( second from the top yellow light) for Good - approx. 12 volts, F (second from the bottom red light) for Fair which according to the creator of the Roadtrek electric simulator in the Notes attachment is approximately 11.3 volts, and L (the bottom red light) for Low at less than 5 volts. The LEDs will give you a fast idea of where the battery voltage might be but there is no way to know how close you are to the light changing to the next lower LED at any time. Only a voltage meter with a display connected directly to the battery line can tell you that.
Bear with me for the why and I promise I will get you to the how. I decided that I wanted to take a reading on the battery voltage that was accurate. With my 2011 190's new design of coach battery compartment, there was no way to pull the batteries out to get to the terminals. The two AGM batteries are bolted with a frame to the inside of the compartment. There is access at the front to one terminal on each battery - a positive and a negative - and the batteries are wired in series. My first thought seeing this was to put the meter on those two terminals. Using the exposed positive and negative terminals I got no reading with my electric multi-meter set to read DC voltage with the scale set to a maximum of 20 volts. I was able to get a reading off of the positive battery terminal using the metal battery frame as a ground. The reading was 6.4 volts. The reading should have been near 12. Inside, the LED panel showed the voltage at the G (yellow) LED. I was getting a reading off of only one battery. This was no good. I would need to get to the rear of the batteries to get a correct reading and that was not possible. The space on top of the batteries is narrow and there is no line of clear sight to the terminals.
There are no 12 volt coach outlets inside the newer Roadtreks. In the past there were 12 volt outlets connected to coach power and it was possible to take a voltage reading from any of those outlets. Some have added a 12 volt outlet using the TV antenna booster wiring located inside of the wall of the top of the inside of the television connection cabinet. This requires taking the booster switch plate off, accessing the connection wires, not shorting the booster switch, connecting a 12 volt outlet to those wires and then making a hole for the outlets wires to come out inside the cabinet. Winegard does make a booster switch with a 12 volt outlet as part of it, but that plate has additional connections that the plate in the Roadtrek does not have. I was not about to start pulling wiring out of anywhere inside the Roadtrek to access 12 volt wiring to get a voltage reading. Sometimes it is best to leave well enough alone.
I get an idea in my head and it is hard to let it go. I wanted to know how this could be done. When I am stumped about RV things - or Roadtrek things - I go to the forums online. On one forum it was confirmed that the 6.4 volt reading was just one of the two batteries. On that same forum it was suggested to me that I could directly access the total battery voltage by going to the connections on the battery separator located under the van's front hood in the engine compartment. The responder "thought" that the left side connection went to the coach battery line.
The battery separator is used on Roadtreks starting in 2006. Previously a battery isolator was used. These two are mechanically different but provide basically the same result - the keep the engine battery and the coach battery apart but still permit the engine running to charge both the engine battery and the coach battery(ies) using the engine's alternator. With this as you drive you charge both the van battery and the coach battery(ies). An aside here, not to confuse the issue at hand, but - if you have a problem with either battery side charging, have this unit checked. They do go bad in time and have caused more unneeded expensive repairs by engine mechanics replacing other things who do not know about RV wiring with the same problem then persisting after their repair work. (So I have been told.)
OK - now that separator is located inside the engine compartment and connected to both the engine battery and the Roadtrek coach battery line. It is located on the top on the rear wall of the engine compartment on the driver's side. I looked in at it and saw that the wires from the batteries were covered with red rubber insulating boots at the connections. I was hesitant to touch these as it appeared that lifting that boot might disconnect the connection. Again, my head said to leave well enough alone - and I did at that point. I was resigned then to give up and just use the LEDs.
I went on one of the Roadtrek Facebook groups on which I had posted about this attempt to find a easy way to get to the coach battery voltage, and said that I was giving up the plan. Jim Hammill, President of Roadtrek, who has at times posted on this group, made comment about using the separator. I replied that I knew about the separator but was reluctant to mess with it. He came back to say that by just lifting the rubber boot a small bit it could not disconnect anything as the connections were bolted on and he confirmed that it was the LEFT side that does, indeed, go to the coach battery connection. By taking a reading from the right side, you are reading the engine battery voltage.
I waited for a day that it was not extremely cold - this is March when this took place, not snowing, and not raining. I was able to get a reading off the separator and the voltage was 11.83. The LEDs inside were only up to the bottom two red LEDs. The second from the bottom is supposed to light at 11.3 volts. So, while the drop from 12 volts was not that significant, it was just about time to charge the Roadtrek batteries with shore power and the weather was cooperating, so I plugged the Roadtrek in and charged the batteries. This brings me - after all of this that you have suffered through reading here to how to do this for yourself. After charging the batteries to full charge, I took another reading which I shall show you how to do! ("Finally, finally! He is getting to the good part!")
FIRST - Go inside and TURN OFF the battery disconnect switch. Take these readings with that switch OFF. Need I tell you, engine off, generator off too!
IF YOUR METER HAS AN ON/OFF SWITCH TURN IT ON. See your meter's instruction book as to how to set it to read DC voltage. Put the meter scale dial on voltage over 12 volts. There should be a 20 volt setting.
Next - open the hood.
Find the Separator. See the next two photos.
NEXT - Gently peel back the red rubber boot on the LEFT SIDE OF THE TOP OF THE SEPARATOR.
See the NUT. Above that nut is a screw bolt. You are going to take the reading on that NUT OR SCREW. The metal coming from under the nut - out from under the red boot does not carry current that will give you a reading. ONLY TAKE THE READING USING THE NUT OR SCREW.
NEXT - Using a voltage meter with probes - positive and negative - you are going to PLACE THE METER POSITIVE (RED) PROB TIP ON THE NUT.
NEXT - PLACE THE METER NEGATIVE PROBE ON A GROUND INSIDE THE ENGINE COMPARTMENT. Most metal connected to the engine compartment is a ground. The simplest thing is find a bolt head that attaches something to the vehicle body.
Here is a nice, easy to find ground right next to the Separator on the right. Despite you see in the photo you are going to touch the probes to their appropriate spot AT THE SAME TIME JUST LIKE THIS --->.