Good Sam RV Travel Guide & Campground Directory

Mark...My Words

Hi, all!

This month's column is all about batteries. Remember to take good care of your RV batteries while your rig is in storage! Keep the water topped up, and make sure they are charged regularly. I wish all of you the happiest of holidays, and I look forward to answering your questions throughout the New Year!


Hey, Mark! I have a newbie question about charging batteries. When I am traveling down the road and my house batteries are not charging, I have to wonder why? It would make total sense to have some of the energy being generated from the motor to go to charging the house batteries. I figure the reason it doesn't is because the battery types are different. Yes, no, maybe? Should the house batteries receive a charge while under way or not? Thanks! Kevin

Hi, Kevin:

The house batteries are 12-volt lead-acid batteries, so the vehicle alternator can charge them just fine. There is no battery-type incompatibility that prohibits it. Most motor homes are set up to charge the house batteries from the engine alternator. The system is really simple: just a wire from the engine battery charging system, through some sort of isolator, back to the house battery bank. The isolator is there to prevent the "house" system from drawing down the starting battery when the vehicle is parked. Trailers are a bit more varied. Most trailers are wired to provide a charge path to the house batteries through the lighting umbilical cord that plugs into the tow vehicle. However, the trailer lighting receptacle on the tow vehicle must be wired properly to take advantage of that option. If you are sure that the batteries are not being charged, some troubleshooting of the wiring is indicated.



When I charge my 12-volt house batteries, max charge is two-thirds. Do I need new batteries?


Hi, Terri:

When you say you are only getting a 2/3 charge, what are you using to determine that? If you are using only the battery monitor that came with your RV, it is likely that it is somewhat inaccurate. The only way to really be sure is to use a decent-quality digital voltmeter to measure the battery voltage. See the chart below. The best way to test your batteries is to leave the RV plugged into AC power overnight, then disconnect it. Make sure that no lights, fans, or appliances are turned on inside the RV, and let it sit for a few hours. Then measure the battery voltage at the batteries. The chart will help you determine what the state of charge actually is. If your batteries are not charging properly, they may be defective. How old are the batteries? If they are several years old, it may be time for some new ones. Have you been keeping the batteries supplied with distilled water throughout their life? Batteries use water, and you must add some every month or two on most RVs. If you haven't been doing so, and your batteries are dry, then they are damaged beyond saving and must be replaced. To learn more about batteries and the maintenance they need, check out my "12V Side of Life" article at

Battery State of Charge



I entered my stored 2007 Kodiak travel trailer to the screech of the LP gas monitor. The unit has been stored for a year with the LP tanks turned off. What steps should I take to diagnose the problem? Thanks, Rick

Hi, Rick:

If there is no propane odor in the RV, and the alarm will not reset, then it is possible that the only problem is that your batteries are low. If the voltage drops far enough, the LP alarm may sound continuously. Check the batteries, or plug the rig into AC power and see if the alarm can be reset. If not, it is likely that the alarm has failed and needs to be replaced. Those alarms do have a service life and should be replaced about every five years


Dear Mark,

In a previous column, you stated that deep-cycle batteries do not like being deeply discharged. I had always been told that was the main purpose of deep-cycle batteries as opposed to automobile types. Was that a typo or has my info been wrong? If regular batteries can be deeply discharged, it would seem to me they would be a better choice in an RV for running the 12-volt equipment. Pete

Hi, Pete:

It's all about battery design: Vehicle starting batteries are designed to provide brief surges of very high current but will quickly fail if they are repeatedly discharged slowly over long periods of time. That's why we use deep-cycle batteries for our RV "house" systems. These batteries are designed to tolerate long, slow discharges and slow recharges. However, most deep-cycle batteries will last a lot longer of they are not discharged until they are almost completely exhausted. A rule of thumb is to keep the depth of discharge to 50 percent or less. The chart above can be used to approximate the depth of discharge. A battery that is routinely discharged only 30-50 percent and then recharged will last about twice as long as a battery that is routinely discharged to 70-80 percent. Running any type of battery completely flat will do irreparable damage to the battery and reduce its working capacity or ability to store energy, so we never want to run them all the way down!


Dear Mark,

I have a 40' 2006 Alpine diesel pusher with a full-size residential refrigerator that runs off the inverter when not plugged in. The batteries run down after four hours, and I have to run the generator to keep it going. I'm thinking about changing my batteries with gel- type of batteries. Do you think this will help? Ada

Hi, Ada:

Standard deep-cycle flooded lead-acid batteries, gel batteries, and AGM batteries all have similar energy density. In other words, they all have similar capacity for a given battery size, so changing to a different type of battery probably won't be the answer. Your residential refrigerator requires a lot of current to operate. If your RV isn't equipped with a fairly large battery bank, say 6-8 batteries or more, there just isn't enough capacity to run everything for very long. Battery bank capacity is measured in amp-hours, and each individual battery only has so much capacity. The way amp-hours work is pretty simple: If you run a single 5-amp load on a 12-volt battery for 6 hours, you will use 30 amp-hours (5 amps X 6 hours = 30 amp-hours). A typical 12-volt deep-cycle battery will have between 150 and 200 amp-hours of capacity. OK so far? Now we need to do a little more math. In order to provide 120VAC power, your inverter has to draw energy from your 12-volt battery bank. For an inverter to make 100 watts of 120VAC power, it takes about 10 amps of continuous current from the battery bank. To run a 500-watt load, it will take 50 amps! Your refrigerator may draw 300 watts or more while running, and then you have to add in whatever else is being operated by the inverter and also any 12-volt lights or appliances that are in use. If your RV already has a large battery bank, then you may have some tired batteries, or there is something else loading the system and causing a larger than normal drain on the batteries. A competent RV mechanic should be able to determine what the problem is.


Mark Nemeth has been involved with all things RV for more than ten years, including almost 5 years on the road as a fulltimer. Nowadays, Mark is parked for a while and works on staff for the Escapees RV club as technical advisor, consumer affairs director, and instructor in the Escapees RVer's Boot Camp program.

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Some content previously printed in Escapees magazine, published by the Escapees RV Club. All material provided by Mark Nemeth, Escapees Magazine Technical Advisor and Boot Camp Instructor. For more information about the Escapees RV Club, please visit or call 888–757–2582.

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