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Old 03-11-2020, 05:13 PM   #1
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Battery Charge Meter

What voltage reading should be displayed for charged batteries in both chassis and house?
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Old 03-11-2020, 05:27 PM   #2
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This is a tougher question than might be immediately apparent.

The very easy answer is that a fully charged Lead Acid Battery should read between 12.6v and 12.7v.

BUT!

Two things will make the battery meter on your RV show you a voltage that's not really the voltage of your batteries.

For a realistic reading on your RV's battery meter you need two things to be true. First, that no charge has been applied to your batteries in the past 30 to 60 mins. Second, you have to be sure that nothing in your RV is using any power from your batteries.

The real world facts are that there is almost no time when you are on your RV and neither of these things are happening.

If you are plugged into shore power, running a generator or even have solar panels on your RV those things are probably charging your batteries.

And, even though you may have all of your 12v lights and appliances turned off it's still possible that other "hidden" devices are using your 12v power.

So, you can turn off your battery disconnect, unplug any charging source and WAIT about an hour and then test your battery voltage level THEN and only THEN will your battery voltage meter display your actual battery charge.
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Old 03-11-2020, 05:27 PM   #3
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Under near zero load with charging removed for at least 1 hour , for flooded lead-acid or AGM full charge will read 12.6 volts.
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Old 03-11-2020, 05:32 PM   #4
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If you don't want to try to orchestrate all of those conditions you can buy a Battery Monitor System (BMS) with a shunt. This will measure all power in and out of your battery bank and give you a true state of charge (SOC) in percentages. And none of the above mentioned conditions apply.

Shunt-based BMS systems are available for as little as $50 and as much as $250. They are generally an easy DIY install item.

There are tons of videos on YouTube about these systems and their installation.
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Old 03-11-2020, 05:34 PM   #5
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Here's a chart that shows battery charge based on voltages:
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Old 03-11-2020, 05:59 PM   #6
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The problem with voltage readings is that they are what we might call "surface voltage" . As away to thin of this, think of adding black paint to clear water. When you look at the water surface, it may look really close to black but give it an hour or two and let that black circulate all around and you may not be able to see much color at all. Certainly not a totally firm explanation but somewhat easier for most of us to understand.
Looking at cars that we are often more familiar with, when the car is running and getting power from the alternator, a voltage check may show near 14 volts and we think we are in great shape, but that is really the higher level put on to charge the battery and when we disconnect the charger and wait a few hours, we may see that the battery has very little charge.
Same goes in reverse when we are pulling power out of the battery. The surface reading may be lower than it actually shows up later if we stop drawing power.
Reading specific gravity of the battery can give a better idea of condition but that gets into the acid testing and not something most should do.
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