Posted by: Mark Polk | 2:25 am

RV DIY Article – Troubleshooting Dead RV Batteries

RV batteries Have you ever gone out to your RV, turned on a light switch or other 12-volt device on and it didn’t work? Chances are if you’ve been RVing for a while this has happened to you. It has probably happened more than once, and the reason is a dead RV battery or batteries.  A common problem with RVs is for the auxiliary or coach battery to drain while sitting in storage. I can’t tell you how many times someone told me that the auxiliary battery died when their RV was in storage, but that there were no 12-volt devices turned on.

There are several things can contribute to this problem.

1) There are numerous electronic devices and equipment in your RV that can drain the coach battery when you’re not using the RV. These parasitic loads can slowly drain the battery when you are confident that nothing was left on. Some examples are the TV antenna booster, the LP gas leak detector and clocks in stereos.  Your automobile has the same type parasitic drains on the battery, but it won’t normally drain the battery completely because you drive the vehicle on a regular basis. On your RV it’s possible for these parasitic loads to drain the battery because you don’t use or charge the battery for periods of time.

2) Another problem is that all batteries self discharge. It’s not uncommon for a battery to discharge up to 10% a month when it sits in storage. The problem again is if the battery is not being used or charged it won’t take long for it to be completely discharged at this rate.

3) In lots of instances you did leave a 12 volt device on by accident and just don’t know it or can’t find what it is that’s draining the battery. We can test for battery drains using a digital voltmeter that has an amp scale to measure current draw.What we are really measuring is resistance. Anything that uses electricity causes resistance or friction in an electrical circuit.

The first step is to make sure the RV is not plugged in. Now we can remove the negative battery cable from the auxiliary battery.  Set the meter to the 10 amp scale. Note: Follow the multimeter instructions and set the meter to read amps. Do not connect the red lead to milliamps (mA) input, it will not work and could damage the meter. With the meter set to measure amps connect the red lead to the negative battery cable you removed, and the black lead to the negative battery terminal itself.  If there is a draw or drain on the battery it will register in amps or milliamps. One amp is equal to 1000 milliamps. Tip: If the meter reads in the 25 to 50 milliamp range  something in the RV is drawing too much power.

To locate the culprit go to the 12-volt fuse panel in the RV and start removing one fuse at a time. When you remove a fuse and the resistance or drain no longer registers on the meter you isolated the item or circuit causing the drain. The fuses are normally labeled so the next step is to see where the problem is. It is usually something simple like a storage bay light or the TV antenna booster that was left on.  In some case locating the drain may require more troubleshooting than this example, but by following a logical sequence you can isolate and correct the problem in most situations. Once you know what circuit is involved trace the circuit until you find the culprit.

3) Some folks think the fix for these battery drain problems is to leave the RV plugged in with the converter charger charging the coach batteries. This will work if your RV is equipped with a more sophisticated 3-stage battery charger, but lots of RVs only have single-stage converter chargers that charge the battery at too high of a rate after the battery reaches a full charge. When this happens overcharging the battery depletes the electrolyte levels creating even more battery related problems.

Sometimes there is no good answer to a problem, but there are recommendations.

One recommendation is to plug the RV in for about 8 hours every week or so charging the batteries until they are topped off, but of course not everybody has a place to plug the RV in. Another recommendation is to remove the batteries when the RV is in long term storage and put them in storage too. The problem with this is you still need to test the battery state of charge every month (remember batteries self-discharge)and  charge any battery that is at or below 80% state of charge. Another recommendation is to purchase some type of battery maintainer & conditioner like a Battery Minder or Battery Tender product that you can leave connected to the batteries without concern of overcharging. Last but certainly not least, you can use and enjoy the RV once a month and let the batteries get charged that way.

Happy RV Learning,

Mark Polk

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  1. On a 5th wheel, check that the little break-away break cable on the hitch is plugged in. This has happened twice to me and it never crossed my mind that it was the issue until stumbling onto it.

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