Friday, June 2, 2023


Avoiding “mysterious” RV battery deaths

By Russ and Tiña De Maris
A dead RV battery is always a frustration, and oftentimes a mystification. Why did it die? RV batteries are good for a limited number of use/charge cycles. As we’ve often commented, the “deeper” you draw a battery down, the fewer use/charge cycles you’ll get out of it. We try (emphasize “try”) not to let our batteries get down to less than half a full charge before we see to it they’re charged up. That’s a big part of the battle right there.

There are “things” that happen, and we’re all familiar with them. Like the time we found our truck camper battery flat for no good reason – until we did a little investigating and found that the clothes closet door latch wasn’t latching right, and the door was open just a skosh. That skosh was big enough to allow the closet light switch to activate, illuminating the empty hanger rod until the battery went south.

Battery parasites

But even with everything in its place, there are mysterious causes of battery failure. We’re not talking about UFOs landing on your RV roof and taking a jump-start for their warp drive. We’re talking parasites.

Like fleas on your dog or cat, these little tiny loads can turn into long-term lifeblood suckers from your RV battery. What are they? One is the circuitry in the LP gas alarm. That little sniffer, sitting there inconspicuously at floor level, draws on your battery 24-7. What else? Some electronic entertainment equipment may draw from your 12-volt system without you being aware of it. Just keeping the memory up in your stereo radio can chew up the volts. There are all sorts of “little” electrical loads that can slowly deplete the battery in your sleeping RV.

What to do? One way of dealing with parasites is to hunt them down and disconnect them. That leads to its own set of problems. Say you disconnect your LP detector – but then forget to hook it up when you hit the road. Then you’re without the protection the detector provides.

Another way is to make sure your batteries are fully charged and then disconnect the battery from the “house” loads. How? Just remove all the wires connected to the negative battery post. When the time comes to hit the road, reconnect the leads and go. Of course, you’ll lose anything in “memory” in electronic devices; you might lose favorite radio “presets.”

You could leave the shore power cable hooked up and hope your power converter will keep the battery charged – without overcharging it. Our fifth wheel converter simply doesn’t keep our battery charged, while in other rigs the converter may “cook” it.

For us, we’ve found the best answer is to leave the rig unplugged, but put a “smart” charger onto the deep-cycle battery. Our smart charger keeps the battery full, but doesn’t allow for overcharging. It also has a pulse system that is said to break up the formation of sulfates on the battery plates – a leading cause of battery failure.




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Tom Runnels
6 months ago

WARNING! If you have a Magnum inverter/charger; do not disconnect the negative battery cable when storing the RV. I used to and the control board went bad in the inverter. When I spoke with Magnum tech support, the tech said it was caused by how I stored the RV. He said always disconnect the positive cable first; never have the positive connected to the inverter without the negative connected. Just the opposite of what we do in automobiles. But for whatever reason, disconnecting the negative while leaving the positive connected, will eventually cause the inverter control board to go bad. I installed a disconnect switch for the positive cable which I now use when storing our RV.

6 months ago

I leave the roof top solar panels hooked up to the Lithium batteries under the bed to keep them problem free.

6 months ago

For my equipment at home and my motorhome house and starting batteries I use a battery maintainer that uses a float and equalizer functions. The float maintains around the 13.2 volts and the equalizer will bump it up to a pulsating 14.2 +/- volts that drives the sulfides off the internal plates. I also am diligent maintaining water levels and connections every month, some of the batteries are approaching 11 years old. If you decide that this type of charger is right for you I suggest that you install a battery isolator switch on the positive post as the 14 volt equalizer could damage sensitivity electronics.

Bob p
6 months ago

Just a technical tidbit parasites don’t “chew” volts, they consume amps.

Bob M
6 months ago

Would have been nice if Russ gave an idea on how long a battery might last with the CO2 detector drawing power. My travel Trailer has been sitting at the dealer for a month because LCI sent a damaged replacement awning to the dealer. Another reason not to buy a RV.

Dick and Sandy near Buffalo, NY
2 years ago

Most of the parasitic draws in our coach come from the four smart TV’s. Turning the TV’s off with the remote does not turn the TV’s or their associated amplifiers or switching boxes completely off and they will continue to draw power while the inverter is on. We need the inverter on to power the residential fridge.
So what we did, when traveling or boon docking and not using the TV’s as overnight, we have hooked up each TV and its associated amplifier and switching boxes on separate electrical power strips of which one has the power for the large Traveler antenna dish.
Depending on what entertainment and other electrical equipment that may have a parasitic draw, electrical power strips may be a way to decrease that draw and give you longer battery life when not on shore power or running the generator. We have also converted over to AGM batteries which hold their charge much longer than regular wet cell batteries.
Stay well, Stay safe.

2 years ago

Add solar. A solar system keeps my batteries charged and allows the small parasitic loads to stay on.

Thomas D
6 months ago
Reply to  Ken

I added I believe a 18 watt solar .it’s big enough to keep batteries charged but not desulfate the plates. So you may still want to use a converter or a battery maintainer. Sulfating will give you proper voltage with a meter but you just won’t get all the amps( current)

Mike & Louise Bacque
5 years ago

A decent battery monitor, and not the one that’s included with the unit, is a must if you’re doing any off-grid camping. Without a decent battery monitor to show Watts or Amp/hrs being drawn and percent of full remaining, it’s like driving a vehicle without a fuel gauge.

Gene Bjerke
5 years ago

In order to minimize phantom loads, when I replaced the CO detector, I bought a battery-powered one, rather than hard-wired. This saves me one phantom draw. I will do the same for the LP detector. I just have to change the batteries the same time as the one in the smoke alarm. I also leave the entertainment center and TV unplugged unless I am using them.

Solar Steve & Liz
5 years ago

A solar charging system can solve this. The charge control must be set correctly for wet or for AGM batteries. If the RV is stored outside, you are all set. If stored in a garage as we do, you can mount one 60-75 watt panel outside and connect, with a charge control, to the battery when in storage. Then when you head out for travel season, that same solar on the garage can be connected to your other vehicles, tractor etc to maintain them during disuse.

Wolfe Rose
5 years ago

I haven’t had a problem with my converter doing its job, but second the external smart charger suggestion. I installed an external 12V socket for outdoor convenience items (12V inflatable pump, vacuum, macerator pump, worklight, etc), so I just jack my BatteryMinder in there when storing RV.

Yes, Mr. Simons, charger is plugged into wall, not loopback into the RV power. I have seen people remove their converter and use only the smart charger in its place, but that requires very conservative battery usage since you recharge slower.

5 years ago

Or you can switch the battery disconnect off.

5 years ago
Reply to  JB

The parasitic loads bypass the disconnect switch and are wired directly to the battery. This is easily testable by turning off your disconnect switch and then using a clamp multimeter to still read the parasitic amp draw in your coach. Multiply that number by 24 and you’ll have the amp hours lost per day and you can estimate how long your batteries will last with the disconnect off before they need a recharge.
(Roughly 40AH for Group 24, 50 for Group27, 55 for Group 31 and 100 for a pair of golf cart batts will leave a fully charged battery at half charge.)
If you want to eliminate parasitics…get a 7 buck negative post disconnector at walmart or amazon etc.
This eliminates having to physically disconnect the wires each time you store the coach.

Ed D.
6 months ago
Reply to  JB

As I found out the hard way, they are not always dependable. I had to replace 2 year old Batteries because the off switch failed to work.

Al Simons
5 years ago

I don’t get it. If you leave your RV unplugged, how does the smart charger get it’s power? Is your smart charger not wired in to your rig’s 120 V system, but powered by just an extension cord?

Bob Bullock
2 years ago
Reply to  Al Simons

A smart charger has to be plugged into an external 120 volt power source, most often one at your storage lot or home.

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