Friday, December 8, 2023


Ask Dave: Can I use tow vehicle battery and jumper cables to supplement my trailer’s house battery?

Dave Solberg is a leading expert in the RV industry and author of the “RV Handbook” as well as the Managing Editor of the RV Repair Club. Today he discusses using a tow vehicle battery and jumper cables to supplement a travel trailer’s house battery.

Dear Dave,
I am traveling to Death Valley next week and staying at Furnace Creek with no hook-ups. I am staying for three nights and have a 120-amp ACOPower solar panel to charge the battery (single 12 volt). It looks like the weather is going to be unseasonably cool with lows in the mid-30s.

While the Suburban furnace runs on propane, the blower motor will be drawing off of house power. I had not anticipated putting this much load on the battery and am worried that I will be using more power than the charger can replenish.

Can I use jumper cables and the battery in my tow car to help keep the travel trailer battery charged? I know when I have jumped cars with dead batteries, there usually is a healthy spark when connecting the jumper cables. I am worried that this might cause a problem with the electrical system of the RV. Is this okay to do? I have a battery kill switch. Should I turn the power to the RV off before connecting the jumper cables from my car to it? Thanks so much. —Michael

Dear Michael,
I spent three nights in Death Valley this past April but did not dry camp; rather, we stayed at the Longstreet Inn, Casino & RV Resort in Amargosa Valley, NV. We shot footage in Furnace Creek as well as Noonday Mine.

We are developing a series of safety videos for off-roading in Death Valley, so be careful and be prepared! First thing, there’s no cell or Wi-Fi service in most parts of the area, so get a satellite phone. Make sure you have a good map and understand the roads and non-roads. There have been several cases of people taking 4-wheel-drive units that they thought were off-road and blowing tires and trying to walk out. They did not make it. If you would like more information, I can put you in touch with the host of the series that has been off-roading in Death Valley for several years.

You are correct in your assumption regarding the 120-watt solar panel not being enough to charge your battery. However, you also need to factor in the amp-hour rating of your battery as well as its current condition as to sulfation. I doubt your battery has more than 100 amp hours, and if it’s lead-acid, you will not be happy with the performance.

I would not suggest using jumper cables from the vehicle to the RV house battery. Not because of damage but, rather, it will drain the battery down fast. You could be stuck with two dead batteries in a place that does not like humans! They call it Death Valley for a reason.

Also, your truck battery is a cold-cranking amp battery and is not designed to drain and be recharged too often. It will ruin it quickly. If you have a-7 pin plug in your vehicle, you should have a charge coming from the engine alternator to the RV as you drive. You could run the vehicle with the unit plugged in, but I would only do that in case of emergency.

I would suggest getting another solar panel and possibly another battery. However, first you need to evaluate the one you already have and match it exactly. If it’s a lead-acid battery and more than two years old, I would purchase two new ones that are AGM and are less maintenance. If you only have one battery, I would assume your converter/charger is not a multi-stage charger and simply throws a 13.6-volt charge to the battery until it reaches 12.6 volts and then levels off to a maintenance charge of 13.2 volts. This does not break up sulfation. You might want to consider one lithium battery as a 100 amp-hour battery will drain down almost 100 percent and your lead acid or AGM only provides 50 percent or less. If it’s sulfated, you’ll be sitting with no battery power in less than a day.

One other consideration: How about a portable generator? Make sure it’s a generator/inverter so it’s got cleaner power (sine). I have found a few at Harbor Freight that have gotten good reviews and are much less expensive. Maybe we can get some of our readers to tell us what they have in the comments. (Readers?)

Now, let’s discuss reducing your 12-volt power consumption, as well. Instead of running your deep-cycle battery-power-devouring furnace, I like to use a catalytic heater that runs on the small propane bottles and uses no battery power.

Again, be careful, stay hydrated, and have fun. Here is the Rubber Foot Buffalo and me at the campsite.

Read more from Dave here


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Acbango (@guest_156713)
1 year ago

I have a predator 3500 from harbor freight. It has been a great little inverter. Super quiet and very efficient. Worth the investment! You could get away with the smaller 2000w inverter with a small trailer.

Harv Dykstra (@guest_155842)
1 year ago

I agree about Longstreets Hotel & RV Park in Amargosa Valley Nevada. Full hookups, beautiful mountain views, and inexpensive, only 20 minutes from the park entrance. We’ve stayed at Longstreets for years. Great place!

Kenneth Fuller (@guest_155781)
1 year ago

I’ve been supplementing my single house battery on my Class C for over a decade without any issues from the starting battery on my toad. I purchased 25′ 4 gauge jumper cables and installed quick-connect ends on them. Since the toad runs nearly everyday, it charges its own battery up completely and when reconnected to the motorhome battery, it transfers energy back into it until the batteries are equalized. You can even let the toad run once hooked up for better charging of the house battery if you’ve depleted them a lot. The other advantage is if generators aren’t allowed, letting the car run for charging purposes shouldn’t be an issue. I’ve never had an issue with my starting battery – still manage to get at least 7-8 years of use out of them.

Michael Theis (@guest_155808)
1 year ago
Reply to  Kenneth Fuller

Kenneth: Thank you for sharing your experience, it is very helpful.

1SG Bernard F. Hoppe USA Retired (@guest_155746)
1 year ago

I’m really disappointed that you did not correct the “heavy spark” cause when connecting the jumper cables. A spark, large or small could be a life changer anywhere near a wet cell battery. Rule #1, always connect a negative cable last and connect it to a grounded metal part away from a battery. AND frozen batteries can explode without a spark.

The Lazy Q (@guest_155765)
1 year ago

Exactly, negative cable goes to a good ground point on the engine…not the battery.

Eddie D. (@guest_155742)
1 year ago

To prevent draining the tow vehicle’s battery, one could let the engine run in idle. Just make sure you have enough gasoline.

Vic (@guest_155741)
1 year ago

Dave, I think Michael meant that his tow vehicle would be running and therefore he would be charging the trailer battery using his alternator. I have done this many times and it works well. I guess the caveat would be that both systems need to be 12 volt, and I’ve only done it with lead acid batteries in both units.
I have also moved the trailer battery into the tow unit temporarily and connected it to the charging system via the cigarette lighter outlet. This way it will charge as you drive. Just make sure that everything is secure and the battery is well vented if necessary.

Crowman (@guest_155758)
1 year ago
Reply to  Vic

Deep cycle batteries shouldn’t been charged over 10 amps. When you charge them with your truck alternator that makes 125 to 225 amps during it’s charging cycle bad things are going to happen to the deep cycle battery.

HappyCamper7424 (@guest_155774)
1 year ago
Reply to  Crowman

Not true, amperage depends on the battery AH rating. Trojan’s website says “When selecting a charger, the charge rate should be between 10% and 13% of the battery’s 20-hour AH capacity. For example, a battery with a 20-hour capacity rating of 225 AH will use a charger rated between approximately 23 and 30 amps (for multiple battery charging use the AH rating of the entire bank). Chargers with lower ratings can be used but the charging time will be increased.” Also, if the alternator really delivered that much amperage to the charging system it would do bad things to the TV battery.

Michael Theis (@guest_155770)
1 year ago
Reply to  Vic

Vic: That is what I was thinking. Charging the trailer battery from my tow vehicle battery with the engine running. Both are lead acid batteries.

Dogman197 (@guest_155810)
1 year ago
Reply to  Vic

Seems like a lot of work. Just upgrade your system with correct or updated batteries and solar panels. Being cheap can come back and bite you in the {bleeped} when you least need it.

Carl (@guest_155738)
1 year ago

I see these catalytic heaters recommended fairly frequently. I would never use one! The vast amount of water vapor emitted from these heaters will likely condense on the cool surfaces of the RV interior, especially in cold temperatures.

Wayne c (@guest_155755)
1 year ago
Reply to  Carl

I Agee catalytic heaters produce a lot of water but in Death Valley where humidity is often in the single digits it may work fine. I use one to take off the morning chill and turn it off when the windows fog up.

Glenn (@guest_155756)
1 year ago
Reply to  Carl

We have used ours extensively in the desert southwest including Death Valley and have never had any condensation issues. Definitely saves a lot of power compared to running the furnace.

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