Friday, October 7, 2022


Dead RV battery issue leaves owner in the dark

By Chris Dougherty
Chris Dougherty is a certified RV technician. Here is a letter about an RV’s house batteries that 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. Those include 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.

Check your DC voltage at the batteries

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 else fails …

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


Ask Dave: My engine battery is dead in 3 days. How do I find the parasitic drain?



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Mike Schwab
8 months ago

Got a voltage meter in my 1997 Ford Ranger. After starting it will read 14.9V. After running for a while it drops to 14.4V. After shutdown it drops under 14V and down to 12.7V for a new battery. My battery after 24 hours will drop to 12.3V, so it doesn’t hold full capacity. No problem starting so it should last a while.

Kyle Petree
8 months ago

7-10 days is about right with parasitic draws. Let’s say there is 1A draw – 24 hours in a day you lose 24AH per day. (Hopefully your parasitic’ s are less than this, but as an easy example.) A single marine battery has around 80AH capacity……

I’d move those parasitic loads to be behind the battery cutoff switch.

Jeff Craig
8 months ago

Is it just me, or shouldn’t every RV’er also have a solar panel or two to keep their batteries topped off? I have a pair of them on my Class A and that keeps the two house and one chassis batteries at 100%. Look for something similar to this:

Ron Lane
8 months ago

In regards to possibly having an inverter and if you do, it must be turned off. Typically, tuning off an inverter at it’s control panel only turns off the control panel….not the inverter itself. Go to the inverter box and see if there is an on/off switch…if not, your best bet is to remove the neg cable from your battery set to isolate it from all the parasitic amperage draws that cause your batteries to go dead.

Dan Cunningham
8 months ago

To say that 12.3 volts is right for an unplugged for an hour battery does not seem right to me. That means your battery is only at 70% of its capacity.

8 months ago

Week to 10 days is too rapid of a discharge. Most automobile batteries will only draw 20-40 milliamps (mA) with key off and will last for months. If you use a 12vdc clamp-on type amp meter and you are indicating a 1 amp draw (1,000 mA) that is horrendous!!! Disconnect the positive post and the negative frame grounding wire while you are gone until you can find the source of this parasitic drain. Heck, I do this when I winterize my 5 battery Class A motorhome and all 5 batteries are ready to go every spring. (24 years of doing this) Good luck.

8 months ago

What Glen says. A battery that shows 12.3v an hour after being charged is seriously deficient, or the charger is not properly charging it. 12.6 is fine, 12.3 not at all.

Glen Cowgill
8 months ago

A fully charged battery is 12.7v. 12.3v is approximately 50% state of charge. When removing the battery from the charger, it will show a surface charge of about 13.2v+ which is the minimum voltage needed to overcome the resistance in the battery for charging. After an hour unplugged, the battery should show 12.7 volts unless there is a load on the battery.

Glen Cowgill
8 months ago
Reply to  Glen Cowgill

I finally found a state of charge chart which shows 12.24V as 60% state of charge so my memory was off 10%.

Rodney Lacy
8 months ago
Reply to  Glen Cowgill

Some batteries need approximately 14 volts to charge 100 percent.