Understanding the the battery power levels - Fiberglass RV


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Old 06-11-2019, 01:18 PM   #1
2B2
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Understanding the the battery power levels

How does one check the power level of the battery in my Casita? Trying to determine how to check my battery power level. It seems that the CO detector will sound when DC power is no longer available, but I would like to know before the battery is dead.
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Old 06-11-2019, 01:59 PM   #2
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Get a digital volt meter and refer to it.

Charge the battery with a smart charger that can be left connected all the time.

When out camping, check the voltage to determine the state of charge. But this is only accurate when the battery is "rested". That simply means there has not been a load on it for a while, maybe 15 minutes to 1/2 hour.

When charging, the charger will take the battery to about 14.1 volts, then go to the next phase.

The next phase is "float" where it will settle to about 13.2 volts and be held there by the charger.

When not on the charger, but fully charged and rested, it will read about 12.69 volts.

The battery should not be drawn down below about 50% during normal use, assuming it is a standard lead/acid battery.

50% of charge is about 12.2 volts. At that level it is time to charge it, or stop the loads.

So, you can watch the charging cycle and determine what is happening by the voltage. Then you can see the state of charge as you use it.

When a load is applied, such as lights, or the heater, the voltage will appear much lower, but that does not indicate the actual state of charge. It must be rested to give an accurate voltage reading.

Small digital meters that plug into a cigarette lighter are very handy. They can be left plugged in and looked at frequently. Or you can install a meter in your electrical panel and switch it on when curious. Morning, when you get up and there has not been a load during the night, is the best time to read the voltage. This gives you an idea of where you stand for the day.

An excellent tool for charging is a suitcase solar system. These can easily make up for all losses if your power demand is low, and you can watch the voltage gradually climb all day.

Be good to your batteries and they will last a long time. If they get run clear down a few times, or are left discharged for a period, their capacity will become much less. If you suspect yours is weak, take it to an auto parts place, or garage, and get it load tested.
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Old 06-11-2019, 02:13 PM   #3
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How does one check the power level of the battery in my Casita? Trying to determine how to check my battery power level. It seems that the CO detector will sound when DC power is no longer available, but I would like to know before the battery is dead.
There are a couple of ways. The easiest is a voltage measurement. There are plug in volt meters that let you know the state of charge. You do have to make the measurement without the converter powering the trailer, and after applying a small (one amp or so) load if you just charged the battery. 12.7V is considered full, 12V half full (which you should not go below if you want your battery to live a normal life) and 10.5V is considered dead.

The voltage measurement will not be accurate if you are plugged in & your converter is charging the battery. Same if you have a solar panel connected.

The most accurate measurement software the state of charge of a battery is to measure the specific gravity of the acid. This is done with a battery hydrometer, and is a pain to do with a Casita since you need to suck out some of the acid in each cell, which pretty much means removing the battery. Still, this is the most accurate method.

If you are willing to invest the $ and the addition of some wiring, a battery monitor such as the Victron or Trimetric battery monitor will let you track the amp hours in & out of your battery, giving you a very accurate measurement of the state of charge.

Unless you do lots of dry camping for days at a time, the simple volt meter will be the least expensive solution & will work well.
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Old 06-11-2019, 02:35 PM   #4
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There are a couple of ways. The easiest is a voltage measurement. There are plug in volt meters that let you know the state of charge. You do have to make the measurement without the converter powering the trailer, and after applying a small (one amp or so) load if you just charged the battery. 12.7V is considered full, 12V half full (which you should not go below if you want your battery to live a normal life) and 10.5V is considered dead.

The voltage measurement will not be accurate if you are plugged in & your converter is charging the battery. Same if you have a solar panel connected.

The most accurate measurement software the state of charge of a battery is to measure the specific gravity of the acid. This is done with a battery hydrometer, and is a pain to do with a Casita since you need to suck out some of the acid in each cell, which pretty much means removing the battery. Still, this is the most accurate method.

If you are willing to invest the $ and the addition of some wiring, a battery monitor such as the Victron or Trimetric battery monitor will let you track at amp hours in & out of your battery, giving you a very accurate measurement of the state of charge.

Unless you do lots of dry camping for days at a time, the simple volt meter will be the least expensive solution & will work well.

What's important to you, anybody, the state of the battery or is there enough battery to last through a 3 day week-end. If the latter, you should know by now. I recently got back from a 6 day trip to one campground, no hookups. By battery lasted without a problem through the entire 6days. I did check the battery at the end of 6 days and I figure I could have gone for few more. I must admit I have very little power drain on the battery. No water pump, no hot water heater, LED light inside, a Furnace that runs a couple minutes a day. The fridge doesn't connect to battery, nor the cook surface. No ceiling fans.




FYI a quick note on voltmeters, Digital meters are always ±1 for the lest significant digit. Explanation If your meter reads 12.5 the actual voltage could be anywhere between 12.4 and 12.6 Also many cheap meters are ±5% of reading. However, this is all not very important when it comes to trailer batteries. If the furnace won't run the batteries is probably too low for the fan to run fast enough to activate the Sail switch.
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Old 06-12-2019, 06:46 AM   #5
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Thanks everyone

I recently purchased a DROK 10-100V Digital Battery Monitor/Capacity Tester, Percentage Level Voltage Temperature Switch Meter Gauge 12V 24V 36V 48V LCD Display Marine RV Battery Power Indicator Panel which needs to be wired directly to the battery. Looks like it will be a bear to program and don't know if this will do the trick. What is your "read" on this type of device?
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Old 06-12-2019, 10:49 AM   #6
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I recently purchased a DROK 10-100V Digital Battery Monitor/Capacity Tester, Percentage Level Voltage Temperature Switch Meter Gauge 12V 24V 36V 48V LCD Display Marine RV Battery Power Indicator Panel which needs to be wired directly to the battery. Looks like it will be a bear to program and don't know if this will do the trick. What is your "read" on this type of device?
Looks like way more information than I need. Fun if you are an enthusiast who likes to watch meters and batteries and such. I have no interest in programming my volt meter or having it calculate my theoretical usage. All you really need is voltage. Over time, you get the general character of the system and have a good idea of how long you can go without re-charging. Or, if you have solar, you can find the balance of increasing or decreasing capacity in the batteries. All with simple voltage readings once in a while.

Break your usage down into how many days it takes to run the batteries down and what kind of use it was. Such as heater use, several movies per night, only lights and water pump, etc. Just a casual accounting of the general conditions, and how long it took to deplete the battery. This isn't in the form of a log book, or spread sheet, but just being aware of a general pattern. Watch the voltage and when it gets to 12.2 (rested), you have an idea of your usage, the time it took, etc.
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Old 06-17-2019, 10:28 AM   #7
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Where do you plug in the voltmeter?

As I read through the great suggestions, it occurred to me "how do you check the volts without removing the battery each time I want to know the voltage?
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Old 06-17-2019, 11:05 AM   #8
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As I read through the great suggestions, it occurred to me "how do you check the volts without removing the battery each time I want to know the voltage?
The easiest way to track the voltage is with a cigarette lighter volt meter. Here is an example of one, but there are a lot of choices.

I've had one of these for years (different model) and it makes reading the voltage very easy. You can also get them with USB plugs built in.

These meters are for the ones of us that may not have the most high-tech 12v panel and just want to see the voltage at a glance. I normally leave mine plugged in all the time when we are out.

These will tell you if you are charging, or not, and what the state of charge is, such as, 50% when reading 21.2 on a rested battery, or 14.1-14.4 at the end of the bulk charging phase., or 13 volts and above, during the day, means the solar is working. Take your readings when there is no load on the battery and it has had a bit of time to rest. But taking the reading while the solar is working, or the generator is working, or the seven pin is connected, will confirm you are charging.

There is a surprising amount of information available from such a simple device. And it uses so little power that it is not necessary to unplug it until you get home.

https://www.amazon.com/INNOVA-3721-B...CJ33JRBM4TNPFK
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Old 06-17-2019, 11:36 AM   #9
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Use the system I described above first. Then if you want to go more high-tech, or more "accurate" later, you can, with a much more complicated and expensive system.

The simple digital volt meter system is all you need for for normal use. After a while, you'll see how much battery the heater uses, how many days of normal use the system can go for, etc. Then you can make adjustment to your use as needed. You might check the voltage early each morning and again last thing at night. This will give you an idea if there was a net gain or loss per day.

My wife, for instance, takes thousands of pictures and is always charging the computer, her phone and a camera. I'm likely to watch a movie in the evening if I can't sleep or am just relaxing. If it's cold, the heater will cycle on and off occasionally. Three days of this kind of use and we are ready to re-charge. If no heater, a week is OK.

If you later go to a monitoring system that keeps track of power in and out, and predicts the remaining power, it may gradually become inaccurate as the batteries sulfate. Unless it can also learn the changing rate of charge and discharge it sees per input and load. I prefer to just sort of get a feel for it and it becomes pretty easy to know where the battery stands on available power. Also, if you move around every few days, the bats will get charged each time you drive, so usage can be higher while stopped, or watched less carefully.

Start out simple. Then move up if you need more information.

This same theory applies to tire and hub temperature monitoring. Some claim you need the most accurate digital infrared thermometer you can buy to prevent garbage in garbage out readings, and then a temperature chart to refer too. When in reality, all you need do is touch each tire and each hub with your hand. This tells you if they're the same or not and if they are getting too hot. If you can hold your hand on them, they are fine. If one is different, it's time to find out why.
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Old 06-17-2019, 11:52 AM   #10
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Where do you plug in the voltmeter?

Raspy,
Your suggestion sounds like a method I will use. Thank you again.
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Old 06-18-2019, 07:52 PM   #11
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Break your usage down into how many days it takes to run the batteries down and what kind of use it was. Such as heater use, several movies per night, only lights and water pump, etc. Just a casual accounting of the general conditions, and how long it took to deplete the battery. This isn't in the form of a log book, or spread sheet, but just being aware of a general pattern. Watch the voltage and when it gets to 12.2 (rested), you have an idea of your usage, the time it took, etc.

I just got six days of use out of my Group 27 battery. The water pumps seem to draw the biggest load. I used the heater each night but only for a few cycles - 10 minutes per night? I have LED lights in all but the reading lamps and used those lamps 1 hour per night, each. The rest of the load on the battery were the water pumps, both for fill and for drain purposes.


My battery got down to 12.2 and lingered there for the last two days. I kept a close eye on it but all was well in the end. I did NOT run the refrigerator until traveling home, when I was plugged into the TV and using 12V for cooling the refrigerator.


I hope this helps.
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Old 06-22-2019, 11:10 AM   #12
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Name: Louis
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how to tell what your batter voltage is

for a very few dollars you can buy a digital led volt read out.
I have one in my big foot and its great you always know the voltage.
and its a great green night light.
It does not tell you the amp hours which is actually more important, but voltage is a big help
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