Wednesday, April 30, 2014

Checking the Coach Batteries Voltage

 In 2011 Roadtrek changed the batteries used for the coach - the living area of your Roadtrek - from wet cell batteries to AGM batteries. As I have written before in various articles, AGM batteries are maintenance free meaning they do not have to be checked to see if the fluid level in the battery is good. In the process of the change to AGM batteries, the battery compartment was changed as well in the 190 and, I presume, the 210. I do not know about the Sprinter Roadtreks. The Sprinters now, also, have AGM batteries but I am not familiar with the Sprinter battery compartment. The change to the 190 battery compartment - which has, and has had, two coach batteries - was the elimination of a second battery compartment for the second battery that was located over the rear passenger tire, and a redesign of the battery compartment located in front of the rear passenger tire which eliminated the sliding shelf floor. Previously, when that compartment was opened, you could pull the sliding shelf out and access the top of the battery. This made it possible to check the battery fluid level easily and also made it possible to put a voltage meter's probes onto the battery to check the full voltage level of both coach batteries. With the AGM batteries there was no longer a need to check the fluid levels, but there is still a need to get an accurate check of the battery voltage.

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 --->.

NOW, look down at your meter. There is a convenient ledge at the front of the engine compartment to set your meter on to see it easily.

The reading - after 22 hours of charging the batteries on shore power is 12.58. For an inexpensive multi-meter, that reading is good enough. I had expected to see 12.8 which was a voltage mentioned to me on one of the forums for fully charged batteries. This reading was taken about two hours after the shore power was disconnected. Inside the Roadtrek the LED panel was on all LEDs to the top C LED which not only indicates Charging but will also stay lit for a period of time - as short as a few hours or as long as a day - because of residual charge still remaining from the charging process. And as noted above when describing the LEDs on the panel, will light when the voltage is at or above 12.7 volts - here we have 12.58 and that is very, very close to 12.8. Very good!


TURN OFF your meter. 


CLOSE the hood. 

YOU ARE DONE - and you now have an accurate reading of the coach battery voltage.

You can now do this whenever you want to find out more than the wall monitor panel LEDs will tell you. A voltage meter like this can be found in stores that sell electric components including the big box home stores. You can find one at Walmart in the electric section of the hardware aisles. This one comes from Harbor Freight stores and if you are lucky enough to find one of the many coupons that the put in many magazines and newspapers or get on their email list, you can have this meter for free with the coupon and any purchase. The meter is just the same as that sold in Walmart and the lower priced meters in the other stores and is good enough for this purpose. There are also the older dial meters that will do the same thing, but it is easier to get a clear reading on a digital screen than it is to decide where the needle is exactly pointing on the scale. 

It is important to note for you that with the meter that I used - and perhaps all such meters - the reading is not instantaneous. The numbers on the screen seem to go all over the place low to higher until is stops at the final reading - which as you see in the photo above, stopped and stayed on 12.58 volts.

So there you are. Even with a newer 190 - or perhaps 210, Ranger, and Sprinters too, you have access to a direct spot to read the voltage of your coach battery(ies). 

And thanks to Meryl who took the photos of my hands holding the probes and also the meter reading!


  1. Robert,
    You sure have come a long way from just before you got your roadtrek and thought the air conditioner ran on the battieres in the posts you did to rvnet.

    Your site is tremendous and you have become very knowledgeable.

    good for you

  2. Makes me glad my 2013C190V has the 12 volt outlet in the TV cabinet. I have a voltage readout mounted there.

    1. Was the 12 volt outlet in your 2013 190 installed at the factory or was it installed aftermarket? I know that a number of Roadtrek owners use the antenna booster 12 volt wiring in that cabinet to install a 12 volt outlet.

  3. My family and I recently purchased a Roadtrek. Thank you for the information about the battery. I am not at all mechanically inclined and am going to use the information to earn some brownie points with my husband. :)