Why do new RV batteries show only 3 of 4 lights green on monitor? Plus update

Dear Dave,
After replacing the two lead acid batteries with deep cycle lead acid, my battery meter only shows three out of four lights green. It was charging at 13.6 when I installed them. Even after a couple days it still shows three out of four lights coming on, indicating it’s three-quarters charged. —Phil, 2018 Heartland Cyclone 4151

Dear Phil,
There are several variables that can cause the monitor panel to only show three out of four lights. First, I am not a fan of the basic four lights showing the State Of Charge (SOC) of a deep cycle battery. Since there are so many charge profiles of flooded lead acid (FLA), absorbed glass mat (AGM), and lithium, it would be difficult to accurately show the SOC, in my opinion.

Battery monitor panel

This is a typical monitor panel shown in a Heartland owner’s manual. It has technical readings of Low, Fair, Good, and Charged. Since you indicated the converter is charging at 13.6 volts, you must be using a multimeter to measure it more accurately. I would suggest plugging the unit in to a 30-amp outlet for 24 hours. The 13.6-volt charge is an indication the batteries are low and the converter is providing a full initial charge.

When the batteries reach 12.6 volt, they are fully charged and the converter should drop to a maintenance charge of 13.2 volts. If your voltage does not drop to the maintenance charge level after 24 hours, you might have a bad cell or defective battery.

Make sure you check the fluid level, as low fluid below the plates would keep it from becoming fully charged.

Recommend using multimeter

I would also recommend unplugging the unit and letting it sit for a few hours to let the “surface charge” wear off, then check it with a multimeter. 12.6 volts is a fully charged FLA battery. Anything less means a low SOC, and most likely a defective battery. Even the cheapest multimeter is better than the LFGC lights.

This meter is reading a battery connected to a Progressive Dynamics converter that is programmed for 13.8 volts for 8 hours.

Update

I sent Phil the rough draft of the above post and got this back from him right away:

Thank you for your insight. The battery issue was rather simple. I had forgotten to turn the master disconnect switch back on after battery installation. When I did, all four lights came on. Before I did that, however, I did disconnect the batteries from one another and do a load test on them. They are both good, as expected, as I just purchased them.

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Is there an RV battery monitor that works?

Dear Dave,
I recently put my rig in storage and within two weeks, the house batteries went dead and the disconnect switch was OFF. Prior to storage, I was plugged into shore power at a park where my battery charge lights showed full charge. Apparently, they must show full charged when plugged into shore power. Is there a “meter” that I can connect to the batteries which would show their actual charge? Something that I could mount in the rig to check the charge. Thanks. —Michael, 2017 Forest River Georgetown

Read Dave’s answer.

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Dave Solberg is a leading expert in the RV industry and the author of the “RV Handbook.”

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