Why do new RV batteries show yellow bars at 12.4 volts with everything off?

Dear Dave, 
I recently bought two Interstate Group 27 deep cycle RV batteries and had the RV shop install them. I picked up the motorhome and took it straight to storage and shut off the power switch at the stairwell. Four weeks later I turned the switch back on and noticed the monitor was showing yellow bars at 12.4 volts.

I brought the motorhome home and turned the switch back on and plugged into shore power. The monitor showed green bars at 13.2. Are the batteries fully charged? Or should I leave them plugged in for 24 hours for full charge? —Keith, 2023 Forest River Georgetown 31L5

Dear Keith,
A fully charged Interstate flooded lead-acid (FLA) battery should read about 12.6 volts at rest. Even with the power switch turned off—assuming this is the battery disconnect—there can still be a small electrical draw. For example, the LP leak detector is typically wired directly to the battery and bypasses the disconnect switch. It usually draws about 0.1–0.5 amps, which may seem minimal but can discharge the battery over the four weeks you mentioned.

RV battery state of charge

At 12.4 volts, your battery is roughly at 70% state of charge (SOC). That level normally wouldn’t fall into the “yellow” range, though meter readings can vary.

Even without any external draw, FLA batteries naturally self-discharge when left without a maintainer. At room temperature, they lose about 3–5% per month, and the rate increases in warmer conditions. Given that your battery dropped to 12.4 volts over four weeks, a small continuous draw—like the LP detector—is likely contributing.

When you plugged the rig in at home, the converter began charging the batteries. If the SOC had been much lower, you likely would have seen around 13.6 volts initially. Since you’re seeing 13.2 volts, that suggests the converter is in a maintenance (float) mode.

Winnebago had Progressive Dynamics customize their converters for FLA batteries at 13.8 volts for 6 hours to help break up sulfation.

I would suggest leaving the rig plugged in overnight and then check the SOC with the shoreline cord unplugged. This will shut off the converter and give a true reading of the batteries only. It would also be a good idea to check the SOC periodically during storage, or install a battery maintainer.

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DAVE HAS ANSWERED MORE THAN 1,000 readers’ maintenance and repair questions. Read a directory here. There is so much to learn!

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

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