Friday, September 17, 2021
Friday, September 17, 2021

Dead RV battery issue leaves owner in the dark

By Chris Dougherty
Chris Dougherty is a certified RV technician. Here is a letter he received from a reader while he was serving as’s technical editor.

Dear Chris,
I have a perplexing issue on my 2012 Holiday Rambler Vacationer. When I put the coach away in storage I carefully make sure the power switch is off for the house batteries. When I return in a week or 10 days, the batteries are depleted. I cannot find or think of any device or thing that is left on that could do this when the switch is off. The batteries are topped up and only about a year-and-a-half old (two Interstate deep cycles). Any tips on how to troubleshoot this, or ideas???  —Bill G

Dear Bill,
Thanks for writing in. It is not uncommon for the batteries to be depleted over a longer period of time, but not that short a time.

RVs will often have components wired directly to the batteries, bypassing the master switch, like propane gas and carbon monoxide detectors, the memory circuit for a stereo, etc. Most of the time these parasitic loads are less than a couple of amps. Evidently, something else is going on.

The first thing to do is to check DC voltage at the batteries when the coach is plugged in and when it’s unplugged. This will determine if the converter/charger is operating properly. A reading of 12.3 VDC or so is right for a coach that’s been unplugged for, say, an hour. When the coach is plugged in, an average of mid to upper 13’s is about right depending on the charger system, and if it’s a multi-stage charger, what stage it’s in. If the batteries are not being fully charged while the coach has an outside power source, then this could contribute to the problem

The next thing to do is, after charging, disconnect the coach from the power source and turn off the battery switch. Then, with a DC amp clamp-type meter, you can check the positive leads from the batteries to see what the amp draw on the battery bank is when everything is supposed to be off. Be sure to include not only the large cables, but any smaller conductors that are attached to the batteries directly. If an amp draw is found, then track it to its source.

Lastly, I would check to make sure the batteries are clean, full of distilled water and the terminals are tight. Loose and corroded terminals can cause similar symptoms.

If all this fails, then its time to have the batteries tested by your Interstate Battery dealer.

Oh, one last thing. I don’t think your coach has an inverter/charger, but many of those coaches did … usually a larger battery bank came with it. Please make sure the inverter is OFF because the inverter/charger common in many of those coaches is connected directly to the battery and could still drain them.

Hope this helps! —Chris

##RVT790 ##RVDT1314


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1 year ago

I do not rely on the power switch because I have found , after owning 3 RV, there is something alway powered even with the power switch off. I keep a racket right by the battery to disconnect the negative terminal. Having a racket readily available next to the battery makes it no big deal to reconnect/ disconnect.

Larry & Bev Lee
1 year ago

Hey guys I’m new to the pull trailer world, My question is we have a new 2020- 26′ Gray Wolf, Am I better off going with 2 6v batteries in series, or just the one 12v Interstate offered at the sale.

1 year ago

Larry and Bev,

The answer depends on how you plan to use the rv. If you want to go boondocking a lot then 2 will be much better than 1 (and probably necessary too). On the other hand, if you are staying in rv parks with shore power then one battery will suffice. Congratulations on buying your new trailer!

Dennis Reiner
1 year ago

Hi Guys, I have a 1999 Forest River Class A motorhome (purchased new) with 4 house batteries and 1 starting battery. I always turn off the master switch in the coach then disconnect the Positive terminal of the starting battery. I then disconnect the Negative frame grounding nut and three Positive leads that feed the house.(my 4 house batteries) Those leads are on a wing nut terminal. I separate all leads with sandwich baggies to prevent any current going thru. All parasitic draw is reduced to micro-amps! (normal car battery parasitic draw in 40-50 milli-amps) Batteries stay fully charged all cold Michigan winter. Note: I occasionally Dremell drum sand ALL my terminal ends to keep them charging correctly and juice flowing freely. THIS IS AN ABSOLUTE MUST. An ohm meter can test resistance for “scummed up cables/terminals”. I keep several new #2 gage x 12″ long red and black battery connectors on hand for regular change-outs linking the 4 house batteries. This all sounds like a lot of work but it takes less than 3 minutes to do this whole routine. I keep all required tools in a small container. This method has been working great for 20 years!!!

1 year ago

I fought low house batteries in my new Berkshire coach for weeks, installed new shutoff switch, checked battery connections etc. Finally bought a 140w Zamp solar panel unit , hooked up directly to batteries and solved the problem. The parasitic draw was the issue.

1 year ago

I’m afraid this is a VERY common problem, and is unlikely to be solved short of installing a battery disconnect on the house battery bank. The “salesman switch” almost never disconnects all the loads on those batteries, and they WILL drain over time. Many of us have decided that the simple solution is finding a way to always have the coach connected to SOME shore-power when it’s in storage. Even a 15a connection is plenty to keep the batteries topped up. Can’t do that? then the disconnect is your only real solution…

1 year ago

A 1 amp parasitic draw is 24 amp-hours a day. My chassis batteries are hit by 1.5 amp draw – I’ve traced to two fuses that run into the dash. 3-4 days parked is enough to kill the battery. While house batteries have more capacity, it’s not unreasonable to see them run down in ten days if they aren’t fully disconnected. My solution was solar plus a Toad battery charger from house batteries to chassis.

Judy and Mark Wiemer
4 years ago

I have a similar problem with my 2016 Holiday Rambler Vacationer as Bill G. but it’s not the house batteries, it’s the chassis. I store my coach and do all the right things. Within TWO days my chassis battery is depleted and I have to use the battery booster to start the motor, what am I doing wrong?

Mel Goddard
4 years ago

Last Oct. I replaced my Parallax converter with a Progressive PD-4655 to maintain and charge my two relatively new Interstate 12V Batteries over Winter.
When I checked the SG last week both were in the Red at 1.200 and below. VDC WAS 12.5 on bat. Pwr. and 13.5 on charge.
The dealers question was:” Is the Hydrometer calibrated for Deep Cycle batteries”?
Never heard of such a thing.
I understand that ALL batteries used the same acid; the difference being construction of the internals.
Was his question valid?

1 year ago
Reply to  Mel Goddard


No, your thought is correct. A hydrometer isn’t calibrated to battery types. They are referring to the charger profiles. When you say your new Progressive unit is used to maintain and charge do you keep your rv plugged in all winter long? If so, it’s likely the batteries have sulfated and are not accepting the charge anymore. When you sample the acid are one or more of the cells reading lower than the rest? If yes, than they need to be replaced. When you solve the issue make sure you use a battery switch that truly disconnects the batteries- allowing no parasitic loads to exist. Just fyi- I just shut off the batteries when I’m done camping. Months later they are still good on charge. If your rig is working properly you shouldn’t have to keep the charger going all the time.

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