Starting battery croaks in campground

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

Dear Chris,
Speaking of batteries — how come my under-the-hood engine battery keeps going dead when I am hooked up to an electric post at campgrounds? I have a Class C Jayco 32-foot motorhome with a V-10 450 gas engine. Funny thing also, I find this out when my propane detector starts screaming. It is wired to the engine battery, too. Oh, and there is a metal bar on the battery that I can lift up to disconnect the power to the one post or leave down and connected. Not sure what that is for; heard lots of opinions. —GiGi

Dear GiGi,
Well, let’s answer these one at a time.

dead-battery

The reason your battery goes dead is that it’s not connected to the coach battery’s charging circuit from the factory, and aren’t most of the time. It is a requirement from the chassis manufacturer that the two 12-volt DC electrical systems remain independent. For this reason, the chassis battery can go dead, especially if there are “parasitic” loads attached to that battery like detectors, steps, stereos and generator start circuits.

The knife blade switch was probably installed to disconnect the battery to keep it from discharging when the coach is not in use. While I’m not sure where you live, another frequent issue is that when the battery is discharged in storage and the outside temperature falls below freezing, the battery is frozen solid and destroyed and will never charge properly again.

The fix for all of this is to:

• Make sure you have a good battery. Many auto parts stores and battery distributors can test it for you.
• Install a built-in battery charging system like the Xantrex Digital Echo Charge, which will automatically transfer battery charging power from the coach battery to the chassis battery while the coach is plugged into shore power, keeping that battery up in addition to the coach battery.
• For prolonged periods in storage, disconnecting the batteries is always a good idea, and if it’s a freezing environment, removing them altogether and storing them in a warm location is best.

##RVT773 ##RVDT1267

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Cam
8 months ago

I’d add that TrikLStart also makes an easy to add engine battery charging link from the house batteries. A full charged battery will only freeze at around minus 80 degrees AND the lower the temperature for a disconnected battery…(i.e. lift the connecting bar in this case) the less self discharge. Room temps will discharge a battery at around 10% a month. Outdoors in freezing temps you would only lose a couple of %.
As long as the battery stays about 60% state of charge….you are not gonna freeze at even 20 below. zero so take an occasional voltage reading and all is well till you hit 12.3 volts. No need to remove the batteries. Just plug in if and when needed.

Ray Leissner
8 months ago

On a related question, I own a 5th wheel and the tow vehicle is usually disconnected when connected to the pedestal. Is it correct to assume that, while connected and towing, the vehicle’s charging system is also charging the 5th wheel batteries?

cam
8 months ago
Reply to  Ray Leissner

Ray…the easiest way to know for sure is to check voltage at your 5th wheel batteries with the vehicle running. You should see a voltage reading above 13.2V if your vehicle charging system is charging your batteries.
Note that such charging is minimal and designed to keep things from going dead while you are underway. Taking a half discharged house batt bank and trying to bring it back full from the vehicle connection could easily take more than 24 hours.

Impavid
8 months ago
Reply to  Ray Leissner

To check if your tow vehicle is putting a charge into your RV battery while driving, follow these steps. Start with the RV umbilical cord unplugged from shore power and unplugged from your tow vehicle. Using a voltmeter set to DC current check the voltage of your RV battery. It should be in the 12 volt range at minimum. Plug your umbilical cord into the tow vehicle and start the engine. Your volt meter should now be reading higher than in the first step. If it is, your alternator is charging your RV battery.